Downlink signal reception method and user equipment, and downlink signal transmission method and base station

ABSTRACT

A default subcarrier spacing for use in transmission/reception of a broadcast channel is defined for each frequency range. A base station transmits a broadcast channel in a frequency band, using the default subcarrier spacing defined for a frequency range to which the corresponding frequency band belongs. A user equipment attempts to detect a broadcast channel in the frequency band where a cell search is being attempted, using the default subcarrier spacing defined for a frequency range to which the frequency band belongs.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for receiving/transmittinga downlink signal.

BACKGROUND ART

With appearance and spread of machine-to-machine (M2M) communication anda variety of devices such as smartphones and tablet PCs and technologydemanding a large amount of data transmission, data throughput needed ina cellular network has rapidly increased. To satisfy such rapidlyincreasing data throughput, carrier aggregation technology, cognitiveradio technology, etc. for efficiently employing more frequency bandsand multiple input multiple output (MIMO) technology, multi-base station(BS) cooperation technology, etc. for raising data capacity transmittedon limited frequency resources have been developed.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). A base station (BS) and a userequipment (UE) transmit and receive data and/or control informationscheduled on a prescribed time unit basis, e.g. on a subframe basis. Thedata is transmitted and received through a data region configured in aUL/DL subframe and the control information is transmitted and receivedthrough a control region configured in the UL/DL subframe. To this end,various physical channels carrying radio signals are formed in the UL/DLsubframe. In contrast, carrier aggregation technology serves to use awider UL/DL bandwidth by aggregating a plurality of UL/DL frequencyblocks in order to use a broader frequency band so that more signalsrelative to signals when a single carrier is used can be simultaneouslyprocessed.

In addition, a communication environment has evolved into increasingdensity of nodes accessible by a user at the periphery of the nodes. Anode refers to a fixed point capable of transmitting/receiving a radiosignal to/from the UE through one or more antennas. A communicationsystem including high-density nodes may provide a better communicationservice to the UE through cooperation between the nodes.

As more communication devices have demanded higher communicationcapacity, there has been necessity of enhanced mobile broadband (eMBB)relative to legacy radio access technology (RAT). In addition, massivemachine type communication (mMTC) for providing various services at anytime and anywhere by connecting a plurality of devices and objects toeach other is one main issue to be considered in next generationcommunication.

Further, a communication system to be designed in consideration of aservice/UE sensitive to reliability and standby time is underdiscussion. Introduction of next generation radio access technology hasbeen discussed by taking into consideration eMBB communication, mMTC,ultra-reliable and low-latency communication (URLLC), and the like.

DISCLOSURE Technical Problem

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

With development of technologies, overcoming delay or latency has becomean important challenge. Applications whose performance criticallydepends on delay/latency are increasing. Accordingly, a method to reducedelay/latency compared to the legacy system is demanded.

Also, with development of smart devices, a new scheme for efficientlytransmitting/receiving a small amount of data or efficientlytransmitting/receiving data occurring at a low frequency is required.

In addition, a signal transmission/reception method is required in thesystem supporting new radio access technologies using high frequencybands.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

According to an aspect of the present invention, provided herein is amethod of receiving a downlink signal by a user equipment in a wirelesscommunication system. The method includes: detecting, in a frequencyband, a broadcast channel using a first subcarrier spacing defined withrespect to a frequency range to which the frequency band belongs; andreceiving, in the frequency band, a downlink data channel carryingsystem information using a second subcarrier spacing, based oninformation on the second subcarrier spacing carried by the broadcastchannel.

According to another aspect of the present invention, provided herein amethod of transmitting a downlink signal by a base station in a wirelesscommunication system. The method include: transmitting, in a frequencyband, a broadcast channel using a first subcarrier spacing defined withrespect to a frequency range to which the frequency band belongs; andtransmitting, in the frequency band, a downlink data channel carryingsystem information using a second subcarrier spacing, based oninformation on the second subcarrier spacing carried by the broadcastchannel.

According to another aspect of the present invention, provided herein auser equipment for receiving a downlink signal in a wirelesscommunication system. The user equipment includes a radio frequency (RF)unit, and a processor configured to control the RF unit. The processoris configured to: detect, in a frequency band, a broadcast channel usinga first subcarrier spacing defined with respect to a frequency range towhich the frequency band belongs; and control the RF unit to receive, inthe frequency band, a downlink data channel carrying system informationusing a second subcarrier spacing, based on information on the secondsubcarrier spacing carried by the broadcast channel.

According to another aspect of the present invention, provided herein abase station for transmitting a downlink signal in a wirelesscommunication system. The base station includes a radio frequency (RF)unit, and a processor configured to control the RF unit. The processoris configured to: control the RF unit to transmit, in a frequency band,a broadcast channel using a first subcarrier spacing defined withrespect to a frequency range to which the frequency band belongs; andcontrol the RF unit to transmit, in the frequency band, a downlink datachannel carrying system information using a second subcarrier spacing,based on information on the second subcarrier spacing carried by thebroadcast channel.

In each aspect of the present invention, the downlink data channelcarrying the system information may be transmitted/received using thefirst subcarrier spacing if the information about the second subcarrierspacing is not present within the broadcast channel.

In each aspect of the present invention, the broadcast channel may carryconfiguration information on a search space for receiving controlinformation of the downlink data channel and/or time resourceinformation on a time resource on which the system information istransmitted. The time resource information may include a periodicity atwhich the system information can be transmitted, a time offset betweenthe broadcast channel and a time at which the system information can betransmitted, or a time window in which the system information can betransmitted.

In each aspect of the present invention, the information on the secondsubcarrier spacing may be information indicating one of candidatesubcarrier spacings defined with respect to each carrier range for adata channel.

In each aspect of the present invention, the broadcast channel may carryinformation on a subcarrier spacing for a random access channel.

The above technical solutions are merely some parts of the examples ofthe present invention and various examples into which the technicalfeatures of the present invention are incorporated can be derived andunderstood by persons skilled in the art from the following detaileddescription of the present invention.

Advantageous Effects

According to the present invention, uplink/downlink signals can beefficiently transmitted/received. Therefore, overall throughput of aradio communication system can be improved.

According to an example of the present invention, delay/latencyoccurring during communication between a user equipment and a basestation may be reduced.

In addition, owing to development of smart devices, it is possible toefficiently transmit/receive not only a small amount of data but alsodata which occurs infrequently.

Moreover, signals can be transmitted/received in the system supportingnew radio access technologies.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate examples of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the structure of a radio frame used in the LTE/LTE-Abased wireless communication system.

FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot inthe LTE/LTE-A based wireless communication system.

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS) slot in the LTE/LTE-A based wirelesscommunication system.

FIG. 4 illustrates the structure of a DL subframe used in the LTE/LTE-Abased wireless communication system.

FIG. 5 illustrates the structure of a UL subframe used in the LTE/LTE-Abased wireless communication system.

FIG. 6 illustrates an example of a short TTI and a transmission exampleof a control channel and a data channel in the short TTI.

FIG. 7 illustrates a subframe structure.

FIG. 8 illustrates an application example of analog beamforming.

FIG. 9 illustrates a time-frequency resource of a random access channelaccording to the present invention.

FIG. 10 illustrates an RACH procedure.

FIG. 11 illustrates a performance effect of Doppler frequency spreadaccording to subcarrier spacing.

FIG. 12 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

MODE FOR THE INVENTION

Reference will now be made in detail to the exemplary examples of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryexamples of the present invention, rather than to show the only examplesthat can be implemented according to the invention. The followingdetailed description includes specific details in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

In examples of the present invention described below, the term “assume”may mean that a subject to transmit a channel transmits the channel inaccordance with the corresponding “assumption”. This may also mean thata subject to receive the channel receives or decodes the channel in aform conforming to the “assumption”, on the assumption that the channelhas been transmitted according to the “assumption”.

In the present invention, puncturing a channel on a specific resourcemeans that the signal of the channel is mapped to the specific resourcein the procedure of resource mapping of the channel, but a portion ofthe signal mapped to the punctured resource is excluded in transmittingthe channel. In other words, the specific resource which is punctured iscounted as a resource for the channel in the procedure of resourcemapping of the channel, a signal mapped to the specific resource amongthe signals of the channel is not actually transmitted. The receiver ofthe channel receives, demodulates or decodes the channel, assuming thatthe signal mapped to the specific resource is not transmitted. On theother hand, rate-matching of a channel on a specific resource means thatthe channel is never mapped to the specific resource in the procedure ofresource mapping of the channel, and thus the specific resource is notused for transmission of the channel. In other words, the rate-matchedresource is not counted as a resource for the channel in the procedureof resource mapping of the channel. The receiver of the channelreceives, demodulates, or decodes the channel, assuming that thespecific rate-matched resource is not used for mapping and transmissionof the channel.

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port or avirtual antenna.

In the present invention, a cell refers to a prescribed geographicalarea to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell. Furthermore, channelstatus/quality of a specific cell refers to channel status/quality of achannel or communication link formed between an eNB or node whichprovides a communication service to the specific cell and a UE. The UEmay measure DL channel state received from a specific node usingcell-specific reference signal(s) (CRS(s)) transmitted on a CRS resourceand/or channel state information reference signal(s) (CSI-RS(s))transmitted on a CSI-RS resource, allocated by antenna port(s) of thespecific node to the specific node. Detailed CSI-RS configuration may beunderstood with reference to 3GPP TS 36.211 and 3GPP TS 36.331documents.

Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a cell in orderto manage radio resources and a cell associated with the radio resourcesis distinguished from a cell of a geographic region.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide service using a carrier and a “cell” of a radioresource is associated with bandwidth (BW) which is a frequency rangeconfigured by the carrier. Since DL coverage, which is a range withinwhich the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, the coverage of the node may be associated with coverage of the“cell” of a radio resource used by the node. Accordingly, the term“cell” may be used to indicate service coverage of the node sometimes, aradio resource at other times, or a range that a signal using a radioresource can reach with valid strength at other times.

Meanwhile, the 3GPP LTE-A standard uses the concept of a cell to manageradio resources. The “cell” associated with the radio resources isdefined by combination of downlink resources and uplink resources, thatis, combination of DL CC and UL CC. The cell may be configured bydownlink resources only, or may be configured by downlink resources anduplink resources. If carrier aggregation is supported, linkage between acarrier frequency of the downlink resources (or DL CC) and a carrierfrequency of the uplink resources (or UL CC) may be indicated by systeminformation. For example, combination of the DL resources and the ULresources may be indicated by linkage of system information block type 2(SIB2). The carrier frequency means a center frequency of each cell orCC. A cell operating on a primary frequency may be referred to as aprimary cell (Pcell) or PCC, and a cell operating on a secondaryfrequency may be referred to as a secondary cell (Scell) or SCC. Thecarrier corresponding to the Pcell on downlink will be referred to as adownlink primary CC (DL PCC), and the carrier corresponding to the Pcellon uplink will be referred to as an uplink primary CC (UL PCC). A Scellmeans a cell that may be configured after completion of radio resourcecontrol (RRC) connection establishment and used to provide additionalradio resources. The Scell may form a set of serving cells for the UEtogether with the Pcell in accordance with capabilities of the UE. Thecarrier corresponding to the Scell on the downlink will be referred toas downlink secondary CC (DL SCC), and the carrier corresponding to theScell on the uplink will be referred to as uplink secondary CC (UL SCC).Although the UE is in RRC-CONNECTED state, if it is not configured bycarrier aggregation or does not support carrier aggregation, a singleserving cell configured by the Pcell only exists.

3GPP LTE/LTE-A standards define DL physical channels corresponding toresource elements carrying information derived from a higher layer andDL physical signals corresponding to resource elements which are used bya physical layer but which do not carry information derived from ahigher layer. For example, a physical downlink shared channel (PDSCH), aphysical broadcast channel (PBCH), a physical multicast channel (PMCH),a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid ARQ indicatorchannel (PHICH) are defined as the DL physical channels, and a referencesignal and a synchronization signal are defined as the DL physicalsignals. A reference signal (RS), also called a pilot, refers to aspecial waveform of a predefined signal known to both a BS and a UE. Forexample, a cell-specific RS (CRS), a UE-specific RS (UE-RS), apositioning RS (PRS), and channel state information RS (CSI-RS) may bedefined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A standards define ULphysical channels corresponding to resource elements carryinginformation derived from a higher layer and UL physical signalscorresponding to resource elements which are used by a physical layerbut which do not carry information derived from a higher layer. Forexample, a physical uplink shared channel (PUSCH), a physical uplinkcontrol channel (PUCCH), and a physical random access channel (PRACH)are defined as the UL physical channels, and a demodulation referencesignal (DM RS) for a UL control/data signal and a sounding referencesignal (SRS) used for UL channel measurement are defined as the ULphysical signals.

In the present invention, a physical downlink control channel (PDCCH), aphysical control format indicator channel (PCFICH), a physical hybridautomatic retransmit request indicator channel (PHICH), and a physicaldownlink shared channel (PDSCH) refer to a set of time-frequencyresources or resource elements (REs) carrying downlink controlinformation (DCI), a set of time-frequency resources or REs carrying acontrol format indicator (CFI), a set of time-frequency resources or REscarrying downlink acknowledgement (ACK)/negative ACK (NACK), and a setof time-frequency resources or REs carrying downlink data, respectively.In addition, a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a physical random access channel(PRACH) refer to a set of time-frequency resources or REs carryinguplink control information (UCI), a set of time-frequency resources orREs carrying uplink data and a set of time-frequency resources or REscarrying random access signals, respectively. In the present invention,in particular, a time-frequency resource or RE that is assigned to orbelongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to asPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,respectively. Therefore, in the present invention, PUCCH/PUSCH/PRACHtransmission of a UE is conceptually identical to UCI/uplink data/randomaccess signal transmission on PUSCH/PUCCH/PRACH, respectively. Inaddition, PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB isconceptually identical to downlink data/DCI transmission onPDCCH/PCFICH/PHICH/PDSCH, respectively.

Hereinafter, OFDM symbol/subcarrier/RE to or for whichCRS/DMRS/CSI-RS/SRS/UE-RS/TRS is assigned or configured will be referredto as CRS/DMRS/CSI-RS/SRS/UE-RS/TRS symbol/carrier/subcarrier/RE. Forexample, an OFDM symbol to or for which a tracking RS (TRS) is assignedor configured is referred to as a TRS symbol, a subcarrier to or forwhich the TRS is assigned or configured is referred to as a TRSsubcarrier, and an RE to or for which the TRS is assigned or configuredis referred to as a TRS RE. In addition, a subframe configured fortransmission of the TRS is referred to as a TRS subframe. Moreover, asubframe in which a broadcast signal is transmitted is referred to as abroadcast subframe or a PBCH subframe and a subframe in which asynchronization signal (e.g. PSS and/or SSS) is transmitted is referredto a synchronization signal subframe or a PSS/SSS subframe. OFDMsymbol/subcarrier/RE to or for which PSS/SSS is assigned or configuredis referred to as PSS/SSS symbol/subcarrier/RE, respectively.

In the present invention, a CRS port, a UE-RS port, a CSI-RS port, and aTRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna ports configured to transmit CRSs may bedistinguished from each other by the locations of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the locations of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the locationsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a patternof REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a predetermined resourceregion. In the present invention, both a DMRS and a UE-RS refer to RSsfor demodulation and, therefore, the terms DMRS and UE-RS are used torefer to RSs for demodulation.

For terms and technologies which are not specifically described amongthe terms of and technologies employed in this specification, 3GPPLTE/LTE-A standard documents, for example, 3GPP TS 36.211, 3GPP TS36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP TS 36.331 may bereferenced.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

Specifically, FIG. 1(a) illustrates an exemplary structure of a radioframe which can be used in frequency division multiplexing (FDD) in 3GPPLTE/LTE-A and FIG. 1(b) illustrates an exemplary structure of a radioframe which can be used in time division multiplexing (TDD) in 3GPPLTE/LTE-A.

Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms (307,200T_(s)) in duration. The radio frame is divided into 10 subframes ofequal size. Subframe numbers may be assigned to the 10 subframes withinone radio frame, respectively. Here, T_(s) denotes sampling time whereT_(s)=1/(2048*15 kHz). Each subframe is 1 ms long and is further dividedinto two slots. 20 slots are sequentially numbered from 0 to 19 in oneradio frame. Duration of each slot is 0.5 ms. A time interval in whichone subframe is transmitted is defined as a transmission time interval(TTI). Time resources may be distinguished by a radio frame number (orradio frame index), a subframe number (or subframe index), a slot number(or slot index), and the like.

A TTI refers to an interval at which data may be scheduled. For example,the transmission opportunity of a UL grant or DL grant is given every 1ms in the current LTE/LTE-A system. The UL/DL grant opportunity is notgiven several times within a time shorter than 1 ms. Accordingly, theTTI is 1 ms in the current LTE-LTE-A system.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

FIG. 2 illustrates the structure of a DL/UL slot structure in theLTE/LTE-A based wireless communication system.

Referring to FIG. 2, a slot includes a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. The OFDMsymbol may refer to one symbol duration.

Referring to FIG. 2, a signal transmitted in each slot may be expressedby a resource grid including N^(DL/UL) _(RB)*N^(RB) _(sc) subcarriersand N^(DL/UL) _(symb) OFDM symbols. N^(DL) _(RB) denotes the number ofRBs in a DL slot and N^(UL) _(RB) denotes the number of RBs in a ULslot. N^(DL) _(RB) and N^(DL) _(RB) depend on a DL transmissionbandwidth and a UL transmission bandwidth, respectively. N^(DL) _(symb)denotes the number of OFDM symbols in a DL slot, N^(UL) _(symb) denotesthe number of OFDM symbols in a UL slot, and N^(RB) _(sc) denotes thenumber of subcarriers configuring one RB.

An OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access schemes. The number of OFDM symbols included in one slotmay be varied according to channel bandwidths and CP lengths. Forexample, in a normal cyclic prefix (CP) case, one slot includes 7 OFDMsymbols. In an extended CP case, one slot includes 6 OFDM symbols.Although one slot of a subframe including 7 OFDM symbols is shown inFIG. 2 for convenience of description, examples of the present inventionare similarly applicable to subframes having a different number of OFDMsymbols. Referring to FIG. 2, each OFDM symbol includes N^(DL/UL)_(RB)*N^(RB) _(sc) subcarriers in the frequency domain. The type of thesubcarrier may be divided into a data subcarrier for data transmission,a reference signal (RS) subcarrier for RS transmission, and a nullsubcarrier for a guard band and a DC component. The null subcarrier forthe DC component is unused and is mapped to a carrier frequency f₀ in aprocess of generating an OFDM signal or in a frequency up-conversionprocess. The carrier frequency is also called a center frequency f_(c).

If a UE is powered on or newly enters a cell, the UE performs an initialcell search procedure of acquiring time and frequency synchronizationwith the cell and detecting a physical cell identity N^(cell) _(ID) ofthe cell. To this end, the UE may establish synchronization with the eNBby receiving synchronization signals, e.g. a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS), from the eNBand obtain information such as a cell identity (ID).

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS) in the LTE/LTE-A based wirelesscommunication system. Specifically, FIG. 3 illustrates a radio framestructure for transmission of an SS and a PBCH in frequency divisionduplex (FDD), wherein FIG. 3(a) illustrates transmission locations of anSS and a PBCH in a radio frame configured as a normal cyclic prefix (CP)and FIG. 3(b) illustrates transmission locations of an SS and a PBCH ina radio frame configured as an extended CP.

An SS will be described in more detail with reference to FIG. 3. An SSis categorized into a PSS and an SSS. The PSS is used to acquiretime-domain synchronization of OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization and theSSS is used to acquire frame synchronization, a cell group ID, and/or CPconfiguration of a cell (i.e. information as to whether a normal CP isused or an extended CP is used). Referring to FIG. 3, each of a PSS andan SSS is transmitted on two OFDM symbols of every radio frame. Morespecifically, SSs are transmitted in the first slot of subframe 0 andthe first slot of subframe 5, in consideration of a global system formobile communication (GSM) frame length of 4.6 ms for facilitation ofinter-radio access technology (inter-RAT) measurement. Especially, a PSSis transmitted on the last OFDM symbol of the first slot of subframe 0and on the last OFDM symbol of the first slot of subframe 5 and an SSSis transmitted on the second to last OFDM symbol of the first slot ofsubframe 0 and on the second to last OFDM symbol of the first slot ofsubframe 5. A boundary of a corresponding radio frame may be detectedthrough the SSS. The PSS is transmitted on the last OFDM symbol of acorresponding slot and the SSS is transmitted on an OFDM symbolimmediately before an OFDM symbol on which the PSS is transmitted. Atransmit diversity scheme of an SS uses only a single antenna port andstandards therefor are not separately defined.

Upon detecting a PSS, a UE may discern that a corresponding subframe isone of subframe 0 and subframe 5 because the PSS is transmitted every 5ms but the UE cannot discern whether the subframe is subframe 0 orsubframe 5. Accordingly, the UE cannot recognize the boundary of a radioframe only by the PSS. That is, frame synchronization cannot be acquiredonly by the PSS. The UE detects the boundary of a radio frame bydetecting an SSS which is transmitted twice in one radio frame withdifferent sequences.

A UE, which has demodulated a DL signal by performing a cell searchprocedure using an SSS and determined time and frequency parametersnecessary for transmitting a UL signal at an accurate time, cancommunicate with an eNB only after acquiring system informationnecessary for system configuration of the UE from the eNB.

The system information is configured by a master information block (MIB)and system information blocks (SIBs). Each SIB includes a set offunctionally associated parameters and may be categorized into an MIB,SIB Type 1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB 17 according toincluded parameters.

The MIB includes most frequency transmitted parameters which areessential for initial access of the UE to a network of the eNB. The UEmay receive the MIB through a broadcast channel (e.g. a PBCH). The MIBincludes DL bandwidth (BW), PHICH configuration, and a system framenumber SFN. Accordingly, the UE can be explicitly aware of informationabout the DL BW, SFN, and PHICH configuration by receiving the PBCH.Meanwhile, information which can be implicitly recognized by the UEthrough reception of the PBCH is the number of transmit antenna ports ofthe eNB. Information about the number of transmit antennas of the eNB isimplicitly signaled by masking (e.g. XOR operation) a sequencecorresponding to the number of transmit antennas to a 16-bit cyclicredundancy check (CRC) used for error detection of the PBCH.

SIB1 includes not only information about time-domain scheduling of otherSIBs but also parameters needed to determine whether a specific cell issuitable for cell selection. SIB 1 is received by the UE throughbroadcast signaling or dedicated signaling.

A DL carrier frequency and a system BW corresponding to the DL carrierfrequency may be acquired by the MIB that the PBCH carries. A UL carrierfrequency and a system BW corresponding to the UL carrier frequency maybe acquired through system information which is a DL signal. If nostored valid system information about a corresponding cell is present asa result of receiving the MIB, the UE applies a DL BW in the MIB to a ULBW until SIB2 is received. For example, the UE may recognize an entireUL system BW which is usable for UL transmission thereby throughUL-carrier frequency and UL-BW information in SIB2 by acquiring SIB2.

In the frequency domain, a PSS/SSS and a PBCH are transmitted only in atotal of 6 RBs, i.e. a total of 72 subcarriers, irrespective of actualsystem BW, wherein 3 RBs are in the left and the other 3 RBs are in theright centering on a DC subcarrier on corresponding OFDM symbols.Therefore, the UE is configured to detect or decode the SS and the PBCHirrespective of DL BW configured for the UE.

After initial cell search, the UE may perform a random access procedureto complete access to the eNB. To this end, the UE may transmit apreamble through a physical random access channel (PRACH) and receive aresponse message to the preamble through a PDCCH and a PDSCH. Incontention based random access, the UE may perform additional PRACHtransmission and a contention resolution procedure of a PDCCH and aPDSCH corresponding to the PDCCH.

After performing the aforementioned procedure, the UE may performPDCCH/PDSCH reception and PUSCH/PUCCH transmission as generaluplink/downlink transmission procedures.

The random access procedure is also referred to as a random accesschannel (RACH) procedure. The random access procedure is used forvarious purposes including initial access, adjustment of ULsynchronization, resource assignment, and handover. Random accessprocedures are categorized into a contention-based procedure and adedicated (i.e., non-contention-based) procedure. The contention-basedrandom access procedure is used for general operations including initialaccess, while the dedicated random access procedure is used for limitedoperations such as handover. In the contention-based random accessprocedure, the UE randomly selects a RACH preamble sequence.Accordingly, it is possible for multiple UEs to transmit the same RACHpreamble sequence at the same time. Thereby, a contention resolutionprocedure needs to be subsequently performed. On the other hand, in thededicated random access procedure, the UE uses an RACH preamble sequencethat the eNB uniquely allocates to the UE. Accordingly, the randomaccess procedure may be performed without collision with other UEs.

The contention-based random access procedure includes the following foursteps. Messages transmitted in Steps 1 to 4 given below may be referredto as Msg1 to Msg4.

-   -   Step 1: RACE preamble (via PRACH) (from UE to eNB)    -   Step 2: Random access response (RAR) (via PDCCH and PDSCH) (from        eNB to UE)    -   Step 3: Layer 2/layer 3 message (via PUSCH) (from UE to eNB)    -   Step 4: Contention resolution message (from eNB to UE)

The dedicated random access procedure includes the following threesteps. Messages transmitted in Steps 0 to 2 may be referred to as Msg0to Msg2, respectively. Uplink transmission (i.e., Step 3) correspondingto the RAR may also be performed as a part of the random accessprocedure. The dedicated random access procedure may be triggered usinga PDCCH for ordering transmission of an RACE preamble (hereinafter, aPDCCH order).

-   -   Step 0: RACE preamble assignment (from eNB to UE) through        dedicated signaling    -   Step 1: RACE preamble (via PRACH) (from UE to eNB)    -   Step 2: RAR (via PDCCH and PDSCH) (from eNB to UE)

After transmitting the RACE preamble, the UE attempts to receive an RARwithin a preset time window. Specifically, the UE attempts to detect aPDCCH with RA-RNTI (Random Access RNTI) (hereinafter, RA-RNTI PDCCH)(e.g., CRC is masked with RA-RNTI on the PDCCH) in the time window. Indetecting the RA-RNTI PDCCH, the UE checks the PDSCH for presence of anRAR directed thereto. The RAR includes timing advance (TA) informationindicating timing offset information for UL synchronization, UL resourceallocation information (UL grant information), and a temporary UEidentifier (e.g., temporary cell-RNTI (TC-RNTI)). The UE may perform ULtransmission (of, e.g., Msg3) according to the resource allocationinformation and the TA value in the RAR. HARQ is applied to ULtransmission corresponding to the RAR. Accordingly, after transmittingMsg3, the UE may receive acknowledgement information (e.g., PHICH)corresponding to Msg3.

A random access preamble, i.e., a RACE preamble consists of a cyclicprefix (CP) having a length of T_(CP) and a sequence part having alength of T_(SEQ). Ter and T_(SEQ) depend on a frame structure and arandom access configuration, and preamble formats are controlled byhigher layers. The RACE preamble is transmitted in a UL subframe.Transmission of random access preambles is restricted to be performed oncertain time and frequency resources. Such a resource is referred to asa PRACH resource. PRACH resources are numbered as the subframe numberincreases in a radio frame and the RPB number increases in the frequencydomain so that index 0 may correspond to the lowest PRB and subframe inthe radio frame. In addition, random access resources are definedaccording to a PRACH configuration index (cf. 3GPP TS 36.211). The PRACHconfiguration index is provided through a higher layer signal(transmitted from an eNB).

In the LTE/LTE-A system, a subcarrier spacing for a random accesspreamble, i.e., a subcarrier spacing for a RACE preamble, is specifiedas 1.25 kHz for preamble formats 0 to 3 and 7.5 kHz for preamble format4 (see 3GPP TS 36.211).

FIG. 4 illustrates the structure of a DL subframe used in the LTE/LTE-Abased wireless communication system.

Referring to FIG. 4, a DL subframe is divided into a control region anda data region in the time domain. Referring to FIG. 4, a maximum of 3(or 4) OFDM symbols located in a front part of a first slot of asubframe corresponds to the control region. Hereinafter, a resourceregion for PDCCH transmission in a DL subframe is referred to as a PDCCHregion. OFDM symbols other than the OFDM symbol(s) used in the controlregion correspond to the data region to which a physical downlink sharedchannel (PDSCH) is allocated. Hereinafter, a resource region availablefor PDSCH transmission in the DL subframe is referred to as a PDSCHregion.

Examples of a DL control channel used in 3GPP LTE include a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a UE or UE group and other controlinformation. Transmit format and resource allocation information of adownlink shared channel (DL-SCH) are referred to as DL schedulinginformation or DL grant. Transmit format and resource allocationinformation of an uplink shared channel (UL-SCH) are referred to as ULscheduling information or UL grant. The size and usage of the DCIcarried by one PDCCH are varied depending on DCI formats. The size ofthe DCI may be varied depending on a coding rate. In the current 3GPPLTE system, various formats are defined, wherein formats 0 and 4 aredefined for a UL, and formats 1, 1A, 1B, 1C, 1, 2, 2A, 2B, 2C, 3 and 3Aare defined for a DL. Combination selected from control information suchas a hopping flag, RB allocation, modulation coding scheme (MCS),redundancy version (RV), new data indicator (NDI), transmit powercontrol (TPC), cyclic shift, cyclic shift demodulation reference signal(DM RS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI) information istransmitted to the UE as the DCI. The following table shows examples ofDCI formats.

The PDCCH is transmitted on an aggregation of one or a plurality ofcontinuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide a coding rate based on the status of aradio channel to the PDCCH. The CCE corresponds to a plurality ofresource element groups (REGs). For example, each CCE contains 9 REGs,which are distributed across the first 1/2/3 (/4 if needed for a 1.4 MHzchannel) OFDM symbols and the system bandwidth through interleaving toenable diversity and to mitigate interference. One REG corresponds tofour REs. Four QPSK symbols are mapped to each REG. A resource element(RE) occupied by the reference signal (RS) is not included in the REG.Accordingly, the number of REGs within given OFDM symbols is varieddepending on the presence of the RS. The REGs are also used for otherdownlink control channels (that is, PDFICH and PHICH).

Assuming that the number of REGs not allocated to the PCFICH or thePHICH is N_(REG), the number of available CCEs in a DL subframe forPDCCH(s) in a system is numbered from 0 to N_(CCE)−1, whereN_(CCE)=floor(N_(REG)/9). A PDCCH including n consecutive CCEs may betransmitted only on CCEs fulfilling “i mod n=0” wherein i is a CCEnumber.

In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH can belocated for each UE is defined. A CCE set in which the UE can detect aPDCCH thereof is referred to as a PDCCH search space or simply as asearch space (SS). An individual resource on which the PDCCH can betransmitted in the SS is called a PDCCH candidate. The set of PDCCHcandidates that the UE is to monitor is defined in terms of SSs, where asearch space S^((L)) _(k) at aggregation level L∈{1,2,4,8} is defined bya set of PDCCH candidates. SSs for respective PDCCH formats may havedifferent sizes and a dedicated SS and a common SS are defined. Thededicated SS is a UE-specific SS (USS) and is configured for eachindividual UE. The common SS (CSS) is configured for a plurality of UEs.The following table shows an example of the aggregation levels definingthe search spaces.

TABLE 1 Search space S^((L)) _(k) Number of PDCCH Type Aggregation levelL Size [in CCEs] Candidates M^((L)) UE-specific 1 6 6 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

The control region of each serving cell consists of a set of CCEs,numbered from 0 to N_(CCE,k)−1, where N_(CCE,k) is the total number ofCCEs in the control region of subframe k. In the 3GPP LTE/LTE-A system,a set of CCEs at which a PDCCH can be located is defined for each UE.The UE monitors a set of PDCCH candidates on one or more activatedserving cells configured as serving cells by higher layer signaling forcontrol information. In this case, monitoring means attempting to decodeeach of PDCCHs in a set according to all monitored DCI formats. For eachserving cell on which PDCCH is monitored, the CCEs corresponding toPDCCH candidates m of the search space S^((L)) _(k) are configured by“L*{(Y_(k)+m′) mod floor(N_(CCE,k)/L)}+i”, where i=0, . . . , L−1. Forthe common search space m′=m. For the PDCCH UE specific search space,for the serving cell on which PDCCH is monitored, if the monitoring UEis configured with carrier indicator field then m′=m+M^((L))*n_(CI)where n_(CI) is the carrier indicator field (CIF) value, else if themonitoring UE is not configured with carrier indicator field then m′=m,where m=0, 1, . . . , M^((L))−1. M^((L)) is the number of PDCCHcandidates to monitor at aggregation level L in the given search space.The carrier indication field value can be the same as a serving cellindex (ServCellIndex). For the common search space, Y_(k) is set to 0for the two aggregation levels L=4 and L=8. For the UE-specific searchspace S^((L)) _(k) at aggregation level D, the variable Y_(k) is definedby “Y_(k)=(A·Y_(k)−1) mod D”, where Y⁻¹=n_(RNTI)≠0, A=39827, D=65537 andk=floor(n_(s)/2). n_(s) is the slot number within a radio frame.

FIG. 5 illustrates the structure of a UL subframe used in the LTE/LTE-Abased wireless communication system.

Referring to FIG. 5, a UL subframe may be divided into a data region anda control region in the frequency domain. One or several PUCCHs may beallocated to the control region to deliver UCI. One or several PUSCHsmay be allocated to the data region of the UE subframe to carry userdata.

In the UL subframe, subcarriers distant from a direct current (DC)subcarrier are used as the control region. In other words, subcarrierslocated at both ends of a UL transmission BW are allocated to transmitUCI. A DC subcarrier is a component unused for signal transmission andis mapped to a carrier frequency f₀ in a frequency up-conversionprocess. A PUCCH for one UE is allocated to an RB pair belonging toresources operating on one carrier frequency and RBs belonging to the RBpair occupy different subcarriers in two slots. The PUCCH allocated inthis way is expressed by frequency hopping of the RB pair allocated tothe PUCCH over a slot boundary. If frequency hopping is not applied, theRB pair occupies the same subcarriers.

Recently, machine type communication (MTC) has come to the fore as asignificant communication standard issue. MTC refers to exchange ofinformation between a machine and an eNB without involving persons orwith minimal human intervention. For example, MTC may be used for datacommunication for measurement/sensing/reporting such as meter reading,water level measurement, use of a surveillance camera, inventoryreporting of a vending machine, etc. and may also be used for automaticapplication or firmware update processes for a plurality of UEs. In MTC,the amount of transmission data is small and UL/DL data transmission orreception (hereinafter, transmission/reception) occurs occasionally. Inconsideration of such properties of MTC, it would be better in terms ofefficiency to reduce production cost and battery consumption of UEs forMTC (hereinafter, MTC UEs) according to data transmission rate. Sincethe MTC UE has low mobility, the channel environment thereof remainssubstantially the same. If an MTC UE is used for metering, reading of ameter, surveillance, and the like, the MTC UE is very likely to belocated in a place such as a basement, a warehouse, and mountain regionswhich the coverage of a typical eNB does not reach. In consideration ofthe purposes of the MTC UE, it is better for a signal for the MTC UE tohave wider coverage than the signal for the conventional UE(hereinafter, a legacy UE).

When considering the usage of the MTC UE, there is a high probabilitythat the MTC UE requires a signal of wide coverage compared with thelegacy UE. Therefore, if the eNB transmits a PDCCH, a PDSCH, etc. to theMTC UE using the same scheme as a scheme of transmitting the PDCCH, thePDSCH, etc. to the legacy UE, the MTC UE has difficulty in receiving thePDCCH, the PDSCH, etc. Therefore, the present invention proposes thatthe eNB apply a coverage enhancement scheme such as subframe repetition(repetition of a subframe with a signal) or subframe bundling upontransmission of a signal to the MTC UE having a coverage issue so thatthe MTC UE can effectively receive a signal transmitted by the eNB. Forexample, the PDCCH and PDSCH may be transmitted to the MTC UE having thecoverage issue in a plurality of subframes (e.g. about 100 subframes).

The examples of the present invention can be applied to not only the3GPP LTE/LTE-A system but also a new radio access technology (RAT)system. As a number of communication devices have required much highercommunication capacity, the necessity of mobile broadband communication,which is much enhanced compared to the conventional RAT, has increased.In addition, massive MTC capable of providing various services anytimeand anywhere by connecting a number of devices or things to each otherhas been considered as a main issue in the next generation communicationsystem. Moreover, the design of a communication system capable ofsupporting services/UEs sensitive to reliability and latency has alsobeen discussed. That is, the introduction of the next generation RATconsidering the enhanced mobile broadband communication, massive MTC,Ultra-reliable and low latency communication (URLLC), etc. has beendiscussed. For convenience of description, the corresponding technologyis simply referred to as a new RAT in this specification.

In the next system of LTE-A, a method to reduce latency of datatransmission is considered. Packet data latency is one of theperformance metrics that vendors, operators and also end-users (viaspeed test applications) regularly measure. Latency measurements aredone in all phases of a radio access network system lifetime, whenverifying a new software release or system component, when deploying asystem and when the system is in commercial operation.

Better latency than previous generations of 3GPP RATs was oneperformance metric that guided the design of LTE. LTE is also nowrecognized by the end-users to be a system that provides faster accessto internet and lower data latencies than previous generations of mobileradio technologies.

However, with respect to further improvements specifically targeting thedelays in the system little has been done. Packet data latency isimportant not only for the perceived responsiveness of the system; it isalso a parameter that indirectly influences the throughput. HTTP/TCP isthe dominating application and transport layer protocol suite used onthe internet today. According to HTTP Archive(http://httparchive.org/trends.php) the typical size of HTTP-basedtransactions over the internet are in the range from a few 10's ofKbytes up to 1 Mbyte. In this size range, the TCP slow start period is asignificant part of the total transport period of the packet stream.During TCP slow start the performance is latency limited. Hence,improved latency can rather easily be shown to improve the averagethroughput, for this type of TCP-based data transactions. In addition,to achieve really high bit rates (in the range of Gbps), UE L2 buffersneed to be dimensioned correspondingly. The longer the round trip time(RTT) is, the bigger the buffers need to be. The only way to reducebuffering requirements in the UE and eNB side is to reduce latency.

Radio resource efficiency could also be positively impacted by latencyreductions. Lower packet data latency could increase the number oftransmission attempts possible within a certain delay bound; hencehigher block error ration (BLER) targets could be used for the datatransmissions, freeing up radio resources but still keeping the samelevel of robustness for users in poor radio conditions. The increasednumber of possible transmissions within a certain delay bound, couldalso translate into more robust transmissions of real-time data streams(e.g. VoLTE), if keeping the same BLER target. This would improve theVoLTE voice system capacity.

There are more over a number of existing applications that would bepositively impacted by reduced latency in terms of increased perceivedquality of experience: examples are gaming, real-time applications likeVoLTE/OTT VoIP and video telephony/conferencing.

Going into the future, there will be a number of new applications thatwill be more and more delay critical. Examples include remotecontrol/driving of vehicles, augmented reality applications in e.g.smart glasses, or specific machine communications requiring low latencyas well as critical communications.

FIG. 6 illustrates an example of a short TTI and a transmission exampleof a control channel and a data channel in the short TTI.

To reduce a user plane (U-plane) latency to 1 ms, a shortened TTI (sTTI)shorter than 1 ms may be configured. For example, for the normal CP, ansTTI consisting of 2 OFDM symbols, an sTTI consisting of 4 OFDM symbolsand/or an sTTI consisting of 7 OFDM symbols may be configured.

In the time domain, all OFDM symbols constituting a default TTI or theOFDM symbols except the OFDM symbols occupying the PDCCH region of theTTI may be divided into two or more sTTIs on some or all frequencyresources in the frequency band of the default TTI.

In the following description, a default TTI or main TTI used in thesystem is referred to as a TTI or subframe, and the TTI having a shorterlength than the default/main TTI of the system is referred to as ansTTI. For example, in a system in which a TTI of 1 ms is used as thedefault TTI as in the current LTE/LTE-A system, a TTI shorter than 1 msmay be referred to as the sTTI. The method of transmitting/receiving asignal in a TTI and an sTTI according to examples described below isapplicable not only to the system according to the current LTE/LTE-Anumerology but also to the default/main TTI and sTTI of the systemaccording to the numerology for the new RAT environment.

In the downlink environment, a PDCCH for transmission/scheduling of datawithin an sTTI (i.e., sPDCCH) and a PDSCH transmitted within an sTTI(i.e., sPDSCH) may be transmitted. For example, referring to FIG. 6, aplurality of the sTTIs may be configured within one subframe, usingdifferent OFDM symbols. For example, the OFDM symbols in the subframemay be divided into one or more sTTIs in the time domain. OFDM symbolsconstituting an sTTI may be configured, excluding the leading OFDMsymbols on which the legacy control channel is transmitted. Transmissionof the sPDCCH and sPDSCH may be performed in a TDM manner within thesTTI, using different OFDM symbol regions. In an sTTI, the sPDCCH andsPDSCH may be transmitted in an FDM manner, using different regions ofPRB(s)/frequency resources.

In a new RAT (NR) system, a time unit in which a data channel may bescheduled may be referred to as other terms, for example, a slot,instead of a subframe. The number of slots in a radio frame of the sametime length may differ according to a time length of a slot. In thepresent invention, the terms “subframe”, “TTI”, and “slot” areinterchangeably used to indicate a basic time unit of scheduling.

<OFDM Numerology>

The new RAT system uses an OFDM transmission scheme or a similartransmission scheme. For example, the new RAT system may follow the OFDMparameters defined in the following table. Or although the new RATsystem still use a legacy LTE/LTE-A numerology, the new RAT system mayhave a wider system bandwidth (e.g., 100 MHz). Or one cell may support aplurality of numerologies. That is, UEs operating with differentnumerologies may co-exist within one cell.

<Analog Beamforming>

In millimeter wave (mmW), the wavelength is shortened, and thus aplurality of antenna elements may be installed in the same area. Forexample, a total of 100 antenna elements may be installed in a 5-by-5 cmpanel in a 30 GHz band with a wavelength of about 1 cm in a2-dimensional array at intervals of 0.52 (wavelength). Therefore, inmmW, increasing the coverage or the throughput by increasing thebeamforming (BF) gain using multiple antenna elements is taken intoconsideration.

If a transceiver unit (TXRU) is provided for each antenna element toenable adjustment of transmit power and phase, independent beamformingis possible for each frequency resource. However, installing TXRU in allof the about 100 antenna elements is less feasible in terms of cost.Therefore, a method of mapping a plurality of antenna elements to oneTXRU and adjusting the direction of a beam using an analog phase shifteris considered. This analog beamforming method may only make one beamdirection in the whole band, and thus may not perform frequencyselective beamforming (BF), which is disadvantageous.

Hybrid BF with B TXRUs that are fewer than Q antenna elements as anintermediate form of digital BF and analog BF may be considered. In thecase of hybrid BF, the number of directions in which beams may betransmitted at the same time is limited to B or less, which depends onthe method of collection of B TXRUs and Q antenna elements.

<Subframe Structure>

FIG. 7 illustrates a new RAT (NR) subframe structure.

To minimize a data transmission delay, a subframe structure in which acontrol channel and a data channel are multiplexed in time divisionmultiplexing (TDM) is considered in 5G new RAT.

In FIG. 7, the hatched area represents the transmission region of a DLcontrol channel (e.g., PDCCH) carrying the DCI, and the black arearepresents the transmission region of a UL control channel (e.g., PUCCH)carrying the UCI. Here, the DCI is control information that the eNBtransmits to the UE. The DCI may include information on cellconfiguration that the UE should know, DL specific information such asDL scheduling, and UL specific information such as UL grant. The UCI iscontrol information that the UE transmits to the eNB. The UCI mayinclude a HARQ ACK/NACK report on the DL data, a CSI report on the DLchannel status, and a scheduling request (SR).

In FIG. 7, the region of symbols from symbol index 1 to symbol index 12may be used for transmission of a physical channel (e.g., a PDSCH)carrying downlink data, or may be used for transmission of a physicalchannel (e.g., PUSCH) carrying uplink data. According to theself-contained subframe structure, DL transmission and UL transmissionmay be sequentially performed in one subframe, and thustransmission/reception of DL data and reception/transmission of ULACK/NACK for the DL data may be performed in one subframe. As a result,the time taken to retransmit data when a data transmission error occursmay be reduced, thereby minimizing the latency of final datatransmission.

In such a self-contained subframe structure, a time gap is needed forthe process of switching from the transmission mode to the receptionmode or from the reception mode to the transmission mode of the eNB andUE. On behalf of the process of switching between the transmission modeand the reception mode, some OFDM symbols at the time of switching fromDL to UL in the self-contained subframe structure are set as a guardperiod (GP).

In a legacy LTE/LTE-A system, a DL control channel is TDMed with a datachannel (refer to FIG. 4) and a PDCCH, which is a control channel, istransmitted throughout an entire system band. However, in new RAT, it isexpected that a bandwidth of one system reaches approximately a minimumof 100 MHz. Therefore, it is difficult to distribute the control channelthroughout the entire band for transmission of the control channel. Fordata transmission/reception of the UE, if the entire band is monitoredto receive the DL control channel, this may cause increase in batteryconsumption of the UE and deterioration of efficiency. Accordingly, thepresent invention proposes a scheme in which the DL control channel canbe locally transmitted or distributively transmitted in a partialfrequency band in a system band, i.e., a channel band.

FIG. 8 illustrates a transmission/reception method of a radio signalusing an analog beam. Particularly, FIG. 8 illustrates atransmission/reception method of a radio signal bytransmission/reception analog beam scanning.

Referring to FIG. 8, if an eNB transmits a synchronization signal in acell or a carrier while switching beams, a UE performs synchronizationwith the cell/carrier using the synchronization signal detected in thecell/carrier and discovers a most suitable (beam) direction for the UE.The UE should be capable of acquiring a cell ID and a beam ID(corresponding to the beam direction) by performing this procedure. TheUE may acquire signals, particularly, RS information, transmitted in thebeam direction, for example, an RS sequence, seed information, andlocation, while acquiring the beam ID. The eNB may allocate a group IDto UEs that have acquired a specific beam ID, i.e., UEs capable ofreceiving a DL channel in a specific beam direction. Cell-commoninformation may be temporally/spatially divided on a beam ID basis andthen transmitted to the UE. The cell-common information may betransmitted to the UE by a beam ID common scheme.

Upon acquiring the beam ID in a cell, the UE may receive cell-specificinformation as beam ID or group ID specific information. The beam ID orgroup ID specific information may be information that UEs of acorresponding group commonly receive.

In the multi-beam environment, signal transmission repetition or beamsweeping for signal reception may be considered according to a Tx/Rxreciprocal capability of a transmission and reception point (TRP) (e.g.,eNB) or a UE. The Tx/Rx reciprocal capability is also referred to asTx/Rx beam correspondence (BC) in the TRP and the UE. In the multi-beamenvironment, if the Tx/Rx reciprocal capability in the TRP or the UEdoes not hold, the UE may not transmit a UL signal in a beam directionin which the UE has received a DL signal because an optimal path of ULmay be different from an optimal path of DL. Tx/Rx BC in the TRP holds,if the TRP can determine a TRP Rx beam for UL reception based on DLmeasurement of UE for one or more Tx beams of the TRP and/or if the TRPcan determine a TRP Tx beam for DL transmission based on UL measurementfor one or more Rx beams of the TRP. Tx/Rx BC in the UE holds if the UEcan determine a UE Rx beam for UL transmission based on DL measurementof UE for one or more Rx beams of the UE and/or if the UE can determinea UE Tx beam for DL reception according to indication of the TRP basedon UL measurement for one or more Tx beams of the UE.

The present invention proposes an initial access procedure, whichbecomes different in millimeter wave (mmWave) due to characteristics ofanalog beamforming, operations of the UE and the eNB according to theinitial access procedure, and signaling information/schemes which shouldbe transmitted between the UE and the eNB.

As mentioned previously, FIG. 7 illustrates a transmission scheme of aDL control channel through TDM with DL data or UL data in a broad band.In terms of the eNB, the eNB may transmit the DL control channel overthe entire band, whereas, in terms of the UE, one UE may receive the DLcontrol channel thereof in a partial specific band rather than theentire band. Herein, the DL control channel means a control channelcarrying DL specific information such as DL scheduling, informationabout cell configuration that the UE should know, and UL specificinformation such as a UL grant, as control information that the eNBtransmits to the UE.

Subcarrier spacings used in the NR system may support a plurality ofsubcarrier spacings (e.g., subcarrier spacings of 15 kHz, 30 kHz, 60kHz, 120 kHz, and 240 kHz) having an integer multiple of (or 2^(n)times) a default subcarrier spacing, based on the default subcarrierspacing.

An operation that the UE should first perform to receive a service bybeing associated with a specific system is acquiring time and frequencysynchronization of the system, receiving basic system information, andadjusting a UL timing on UL. This procedure is generally called theinitial access procedure. The initial access procedure generallyincludes a synchronization procedure and an RACH procedure. A briefdescription of the synchronization procedure of the LTE/LTE-A system isas follows.

Primary synchronization signal (PSS): symbol timing acquisition,frequency synchronization, and cell ID detection within a cell ID group(three hypotheses).

Secondary synchronization signal (SSS): cell ID group detection (168hypotheses), 10-ms frame boundary detection, and CP detection (twohypotheses).

Physical broadcast channel (PBCH) decoding: 40-ms timing detection,antenna configuration, system information acquisition, system bandwidth,etc.

That is, the UE acquires an OFDM symbol timing and a subframe timingthrough the PSS and the SSS, acquires a cell ID, and acquires essentialinformation of a corresponding system by descrambling and decoding thePBCH using the cell ID.

It is expected that the NR system will support bands from a lowfrequency band of 700 MHz to a very high frequency band even up to 100GHz. According to characteristics of each frequency band andrequirements/characteristics of a service, different numerologies may beused in the NR system. In addition, different numerologies may besimultaneously multiplexed in the same system or subcarrier/subband. Inthis case, a numerology includes a subcarrier spacing, a (time) symbollength, a subframe length (or slot length), and/or a CP length.

The initial access procedure is an absolutely indispensable procedurewhen the UE connects to a network and multiple steps are involved inthis procedure. The present invention proposes a random access procedurefor the NR system, including PSS/SSS detection, PBCH and other systeminformation decoding, and an RACH procedure.

In the NR system, at least two types of synchronization signalsdescribed below may be used.

1) NR-PSS for at least initial symbol boundary synchronization to an NRcell.

2) NR-SSS for detection of an NR cell ID or at least a part of the NRcell ID. The number of NR cell IDs aims to determine to be at least 504.The number of NR cell IDs may be determined to be equal or greater thanthe number of cell IDs (i.e., 504 cell IDs) in the LTE/LTE-A system.NR-SSS detection is based on a fixed time/frequency relationship with anNR-SSS resource location regardless of a duplex mode and a beamoperation type in at least a given frequency range and CP overhead.

In addition, in the NR system, at least one broadcast channel(hereinafter, an NR-PBCH) may be used. NR-PBCH decoding is based on afixed relationship with NR-PSS and/or NR-SSS resources regardless of theduplex mode and the beam operation type in at least a given frequencyrange and CP overhead. To carry essential system information, thefollowing broadcasting schemes may be considered:

Option 1) The NR-PBCH carries a part of essential system information forinitial access, including information needed when the UE receives achannel carrying the remaining essential system information.

Option 2) The NR-PBCH carries not only the information of Option 1 butalso minimum information needed when the UE performs initial ULtransmission (which is not limited to the NR-PBCH).

Option 3) The NR-PBCH carries all essential information for initialaccess.

In addition to the above options, other options may be used.

A. Initial Access Procedure

<A.1. Step 1: PSS/SSS Detection>

When different numerologies are supported in the same system or samecarrier, a numerology used to transmit a synchronization signal is notfixed and may vary in the time domain or frequency domain. In this case,ambiguity may occur when the UE detects the synchronization signal. Inconsideration of this situation, the present invention proposes anumerology used to transmit the synchronization signal and a method ofdetecting the synchronization signal by the UE.

Fully Blind Detection on SS

A synchronization signal (SS) may be transmitted using the samenumerology as a numerology used for data transmission in a correspondingband. Alternatively, the SS may be transmitted using one arbitrarynumerology among numerologies that a system may support irrespective ofthe numerology used for data transmission in a corresponding band. Inthis case, the UE may blind-detect the SS. For example, if subcarrierspacings that the NR system may support are Δf∈{15 kHz, 30 kHz, 60 kHz,120 kHz, . . . }, the SS may be transmitted using one of the subcarrierspacings that the NR system may support. The UE may attempt to detectthe SS in an arbitrary band using frequency raster thereof. The UE mayattempt to blind-detect the SS with respect to an available subcarrierspacing at every frequency raster location and/or a CP length in eachsubcarrier spacing or attempt to sequentially detect the SS with respectto each subcarrier spacing candidate in a frequency range desired to bedetected.

Detection in Given Set of SS Numerologies

To improve the performance of SS detection and reduce the complexity ofthe UE, a set of numerology candidates used for SS transmission may bepreconfigured. For example, a numerology having a relatively largesubcarrier spacing (SC) may be configured not to be supported in a verylow frequency band (e.g., a band of 700 MHz) and a numerology having arelatively small subcarrier spacing may be configured not to besupported in a very high frequency band. Accordingly, a numerology setavailable for SS transmission may be defined in standardization withrespect to each frequency range or each frequency band. For example, thenumerology set available for SS transmission with respect to eachfrequency band may be defined as follows.

-   -   Numerology candidates in frequency range from f_(n) to f_(m) MHz

1) Option a: {(SC_(i), CP_(i)), i=0, 1, . . . , N}.

The UE attempts to detect the SS based on given candidates of asubcarrier spacing and a CP. That is, the UE detects the SS under theassumption that the SS is transmitted using one of given numerologies ina specific frequency range.

2) Option b: {SC_(i), i=0, 1, . . . , N}, where a CP length is unknown.In this case, the UE blind-detects a subcarrier spacing first in givensubcarrier spacing candidates and blind-detects the CP length.

A plurality of numerologies including a subcarrier spacing, a CP length,and a subframe length is supported in the NR system due to a wide rangeof frequencies and diversified use cases, service demands, and/orrequirements. A subcarrier spacing for a PSS/SSS may differ in eachfrequency range according to frequency characteristics of frequencybands or this may depend on network choice. At least one subcarrierspacing for each SS may be predefined in a specification for a givenfrequency range. In a specific frequency range, the UE may assume that aPSS/SSS/PBCH in a corresponding band is transmitted using a predefinedsubcarrier spacing. However, when multiple subcarrier spacings areapplied to the PSS/SSS in the NR system, the UE should blind-detect thePSS/SSS using different subcarrier spacings in an extremely wide rangeof frequencies, thereby causing UE implementation complexity, UE batteryconsumption, and greater network access latency. Therefore, a singlesubcarrier spacing (i.e., N=0) may be proper for each SS in a givenfrequency range.

Among numerologies defined/scheduled as candidates available for SStransmission in a corresponding frequency band, at least one numerologyshould be a numerology used for data transmission/reception in thecorresponding frequency band.

While the PSS/SSS is transmitted omnidirectionally in the LTE/LTE-Asystem, a method is considered in which the eNB to which mmWave isapplied transmits a signal such as the PSS/SSS/PBCH through beamformingwhile sweeping beam directions omnidirectionally. In this way,transmission/reception of a signal while sweeping beam directions isreferred to as beam sweeping or beam scanning. For example, assumingthat the eNB has a maximum of N beam directions, the eNB transmits thesignal such as the PSS/SSS/PBCH in each of the N beam directions. Thatis, the eNB transmits an SS such as the PSS/SSS/PBCH in each directionwhile sweeping directions that the eNB may have or the eNB desires tosupport. Alternatively, when the eNB may form N beams, one beam groupmay be configured by grouping a few beams and the PSS/SSS/PBCH may betransmitted/received with respect to each beam group. In this case, onebeam group includes one or more beams. A bundle of the PSS/SSS/PBCH perbeam group is referred to as an SS block. In terms of SS transmission,the “SS block” is defined as a container for carrying the PSS, the SSS,the PBCH, and other system information in the NR system. That is, the SSblock is made by a combination of SSs. Although at least one subcarrierspacing may be predefined with respect to the SS, it is necessary todiscuss whether the PSS, the SSS, and the PBCH are to share the samesubcarrier spacing. The SS may be broadly divided, as described above,into the PSS and the SSS according to a role thereof. If the UE performsblind detection (BD) for a numerology used for SS transmission, this mayimply that the UE performs BD for a numerology used for PSS transmissionbecause the UE should primarily detect the PSS first. The UE may detectan ID, which is a seed of a PSS sequence, (e.g., the ID means a cell IDin the legacy LTE system) or candidates of the ID by detecting the PSSand acquire coarse time/frequency synchronization. Next, the UE detectsthe SSS. In this case, a numerology used for SSS transmission may bedifferent from a numerology used for PSS transmission. The followingschemes may be used for numerologies used for PSS/SSS transmission.

-   -   Option 1: The PSS and the SSS share the same numerology. In this        case, the UE first detects the PSS and then detects the SSS        using a numerology used for the PSS. Upon acquiring a subframe        timing and a cell ID/beam ID using the SSS, the UE receives the        PBCH in order to acquire system information. When necessary,        particularly, when the eNB performs beam sweeping of the SS        using analog beamforming, the eNB may cause the UE to obtain an        accurate subframe timing of a corresponding cell by transmitting        an extended SS (ESS). The PBCH means a channel carrying the most        essential system information. A numerology used for PBCH        transmission may be different from a numerology used for PSS/SSS        transmission. This may be associated with beam management of a        transmission and reception point (TRP). If a specific TRP        desires to extend a large number of beam directions used for SS        transmission and beam reference signal (BRS) transmission, i.e.,        if the specific TRP desires to show many beam directions to the        UE, or if the number of beams that the TRP may have is larger        than the number of (time) symbols constituting one subframe, the        TRP may transmit the PSS/SSS having a wider subcarrier spacing        and transmit the PBCH having a narrower subcarrier spacing than        the subcarrier spacing of the PSS/SSS. Alternatively, when UEs        are gathered at a specific location, when the TRP does not have        to transmit the PSS/SSS in all beam directions, when only some        (time) symbols are used for PSS/SSS transmission and other data,        except for the PSS/SSS or a beam related signal (e.g., PBCH,        BRS, etc.), should be transmitted in a duration of the remaining        symbol(s), or when other reasons occur, a numerology and/or a        time-frequency resource used for SS transmission may be        different from a numerology and/or a time-frequency resource        used for PBCH transmission. Hereinafter, a method of configuring        numerologies of the SSS and the PBCH will be described.

1) Alt 1: The PBCH, the PSS, and the SSS share the same numerology. TheUE uses a numerology obtained by detecting the PSS to decode the SSS andthen decode the PBCH.

2) Alt 2: The PBCH has a numerology different from the PSS/SSS. The ESSwhich may be additionally defined and the SSS may indicate a numerologyused by the UE to receive the PBCH. In this case, a numerology valueused for the PBCH among numerology candidate sets available for PSS BDmay be indicated. If a numerology set available for PSS transmission is{a, b, c, d, . . . } (where each of a, b, c, d, . . . denotes anumerology including a subcarrier spacing, a CP length, etc.), anumerology set available for PBCH transmission should be a subset of thenumerology set and, for example, one of {a, b} may be a numerology valueavailable for PBCH transmission. In this case, the SSS or the ESS mayindicate a or b. The UE receives/decodes the PBCH using a numerologyvalue indicated by the numerology of the PBCH. Herein, the UE may assumethat a DL data channel and/or control channel immediately afterreceiving the PBCH uses the same numerology as the numerology used forthe PBCH.

<A.2. Step 2: PBCH Decoding>

The UE acquires time and frequency synchronization and cell IDinformation by detecting the PSS and the SSS. The next step is acquiringessential system information (SI) to access the network. In the NRsystem, the essential SI which is absolutely necessary for the UE toaccess the network is referred to as minimum system information (or Min.SI). The most essential information out of the Min. SI is transmitted onthe PBCH and the other Min. SI is not transmitted on the PBCH (this isreferred to as the remaining Min. SI (RMSI)). Only when the UE receivesup to the RMSI, the UE may access the network by performing a randomaccess procedure.

In other words, in the NR system, at least one broadcast channel(hereinafter, a PBCH) may be defined and the PBCH may be used to carrythe absolutely essential SI (i.e., a part of the Min. SI). Afteracquiring synchronization of the network and the cell ID, the UE isready to decode the PBCH.

A subcarrier spacing predefined in a communication specification for aspecific frequency range is referred to as a reference numerology or adefault numerology for an SS. For the reference numerology within aspecific frequency range, multiple candidates for the subcarrier spacingmay also be predefined in the specification. For example, a subcarrierspacing of an SS/PBCH for frequencies below 6 GHz may be 15 kHz and aset of subcarrier spacing candidates for data transmission, such as{3.75 kHz, 15 kHz, 30 kHz, 60 kHz}, may be predefined. If 60 kHz is usedas the SS/PBCH subcarrier spacing for a frequency range above 6 GHz, aset of subcarrier spacing candidates for a data subcarrier spacing maybe, for example, {15 kHz, 30 kHz, 60 kHz, 120 kHz} and this may bespecified by a communication specification. That is, the defaultnumerology for the SS/PBCH is defined or determined per frequency rangeand a set of numerology candidates for (UL/DL) data is mapped perdefault numerology for the SS/PBCH (or a frequency range). The defaultnumerology for the SS/PBCH may be equal to the default numerology forthe (UL/DL) data. Alternatively, the default numerology for the (UL/DL)data may be tied to the default numerology for the SS/PBCH.

As described above, the PBCH will be transmitted within an SS block andthe subcarrier spacing of the PBCH may conform to the subcarrier spacingof the SS. Since information bits/field composition will be fixed withinthe PBCH, although all of the Min. SI cannot be transmitted on the PBCH,a part of the Min. SI may be transmitted on the PBCH and the rest (i.e.,RMSI) of essential Min. SI (i.e., minimum SI) for initial access may betransmitted on other channels. The PBCH may signal where/when/how theremaining Min. SI (hereinafter, RMSI) can be acquired.

The PBCH of NR (i.e., NR-PBCH) may carry a part of the Min. SI includingconfiguration/scheduling information for the RMSI and other SI. A partof the Min. SI is included in the NR-PBCH. The RMSI is transmitted onother channels and the NR-PBCH may provide configuration/schedulinginformation about the RMSI so that the UE may receive the RMSI.

An issue is how to deliver the RMSI. There may be a few options fordelivering the RMSI. For example, a new channel may be defined as asecond PBCH (hereinafter, an sPBCH) for delivering the RMSI or the RMSImay be delivered within a data channel. If the PBCH is transmittedthrough beam sweeping, the RMSI should be transmitted through beamsweeping because the Min. SI is essential information when the UEaccesses the network. If NR defines a new channel for delivering theRMSI, i.e., the sPBCH, the sPBCH may be multiplexed within the SS block.Alternatively, another round of beam sweeping for sPBCH transmission maybe required although such a round may cause network inefficiency.Notably, while the sPBCH may provide a limited level of MCSs, use of thesPBCH to deliver the Min. SI may damage system flexibility for NRbecause the sPBCH should always be reserved for RMSI transmission.

For system flexibility, the present invention proposes transmitting theRMSI on a PDSCH. The PDSCH carrying the RMSI may be transmitted in unitsof a mini-slot in the time domain in consideration of a beam sweepingoperation for the RMSI. That is, mini-slot based beam sweeping may beapplied to RMSI delivery. Since it is a heavy burden on the UE toperform BD for a control search space in every mini-slot in order toreceive the RMSI, the network should provide information as to when theRMSI is to be delivered. To provide timing information of controlinformation for the RMSI, a specific time (e.g., a slot index)indication may be provided by the NR-PBCH. Alternatively, an implicitoffset for the control information or an offset for a search space inwhich the UE should search for the control information may be known tothe UE based on an NR-PBCH transmission time index (e.g., a slot indexand/or an SS block index). In terms of signaling for a time instance fora control resource, the network may signal a time window in which UE(s)are to monitor the control resource for the RMSI.

To receive SI, NR may configure a non-UE dedicated search space forcontrol channels, which may be SS block-specific or UE group-specific. Asearch space set may be predefined by a communication specification andthe NR-PBCH may signal specific set(s) of a search space for the RMSI.If the RMSI is provided through the PDSCH, a numerology of the searchspace for the RMSI, particularly, a subcarrier spacing, should beidentical to a numerology of the PDSCH carrying the RMSI. Each system ofthe present invention may have a default subcarrier spacing for aPDCCH/PDSCH/PUSCH/PUCCH and the default subcarrier spacing may beprovided through a broadcast channel such as the PBCH or predefined inevery frequency range by the communication specification. The subcarrierspacing for the RMSI may conform to the default subcarrier spacing forthe PDCCH/PDSCH. The meaning of “the PBCH indicates the subcarrierspacing for the RMSI” may imply that the PBCH indicates a subcarrierspacing for data among a plurality of numerologies supported by thesystem/cell. If the PBCH indicates the subcarrier spacing for the RMSI,the subcarrier spacing for data may be immediately applied after thePBCH is decoded. Otherwise, the UE may be aware of the subcarrierspacing for data only after receiving an RAR at the earliest.

Other SI may be transmitted in a similar manner to a scheme of theabove-described RMSI.

<A.3. Step 3: RACH Procedure>

Upon receiving essential SI (i.e., Min. SI), the UE is ready to attemptto perform UL synchronization. Similarly to an SS such as a PSS, an SSS,or a PBCH, a numerology for an RACH procedure should be determined.Considering a target scenario and coverage requirements, since anumerology for a PRACH is different from a numerology for data, anumerology for PRACH preamble transmission is different from anumerology for SSs or data. Details of RACH numerology need to besignaled by SI. Hereinafter, an RACH resource numerology will bediscussed first in terms of a resource unit, i.e., the size of atime-frequency block considering multiplexing of an RACH resource anddata.

A.3.1. PRACH Resource Configuration

For convenience of description, a time/frequency resource on which RACHmessage(s) are transmitted will hereinafter be referred to as an RACHresource. The RACH resource may further be defined as a UL RACH resourceand a DL RACH resource. PRACH preamble and, possibly, UL RACH message 3such as Msg3 may be transmitted on the UL RACH resource. RAR and,possibly, DL RACH message 4 such as Msg4 may be transmitted on the DLRACH resource. Basically, the RACH resource conforms to the size of atime/frequency resource of an SS block and an SS burst. Alternatively,the size and location information on the time/frequency of the RACHresource are included in PRACH configuration.

FIG. 9 illustrates a time-frequency resource of a random access channelaccording to the present invention. Particularly, FIG. 9 illustrates anexample of cell-specific and implicit PRACH resource configuration.

Although the network/eNB may explicitly inform the UE of a PRACHtime-frequency resource on which the UE can transmit a PRACH, the PRACHtime-frequency resource may be implicitly tied to a resource on which anSS is transmitted so as to cause the UE to implicitly be aware of thelocation of the PRACH time-frequency resource. For example, referring toFIG. 9, the time resource of the PRACH may be placed at a specificoffset from a time resource on which the SS is transmitted and thefrequency resource of the PRACH may be placed at a specific offset froma location at which the SS is transmitted (i.e., a location detected bythe UE). In FIG. 9, Toffset(t) may be a function of a subframe or slotnumber in which the SS is transmitted, i.e., a time at which the SS istransmitted, and a cell ID detected by the UE through the SS. Similarly,in FIG. 9, Foffset(t) may be a function of a subframe or slot number inwhich the SS is transmitted, i.e., a time t at which the SS istransmitted, and/or a frequency in which the SS is transmitted, and acell ID detected by the UE. In other words, Toffset(t)=Function(t, cellID) and Foffset(t)=Function(t, f, cell ID).

In this way, the PRACH resource may be cell-specifically configured. TheUE may derive the PRACH frequency resource using the function of thetime/frequency resource on which the SS is transmitted and the cell IDdetected by the UE. For example, a corresponding PRACH time/frequencyoffset value may be a function of the cell ID. When the SS such as aPSS/SSS is transmitted in a plurality of beam directions, acell-specific PRACH resource may be configured beam-commonly orbeam-specifically. For example, the PRACH resource may be beam-commonlyconfigured by tying the time resource of the PRACH resource to asubframe (or slot) in which the SS is transmitted. For example, if asubframe number in which the SS is transmitted is t, the time resourceof the PRACH resource may be beam-commonly configured byToffset(t)=Function(t, cell ID). Alternatively, the PRACH resource maybe beam-specifically configured by tying the time resource of the PRACHresource to a (time) symbol in which the SS is transmitted. For example,when a symbol unit in which a beam is transmitted (e.g., a subframenumber or a symbol number) is t, the time resource of the PRACH resourcemay be beam-specifically configured by Toffset(t)=Function(t, cell ID).

In PRACH resource configuration, PRACH preamble/sequence relatedinformation such as a PRACH preamble index, preamble transmission power,and an RA-RNTI, in addition to the PRACH time-frequency resource, may betransmitted on the PBCH. In other words, PRACH resource configurationrelated information may be transmitted as essential SI. Candidates ofthe essential SI that can be transmitted on the PBCH may includeinformation about a numerology used to receive a DL/UL data/controlchannel in addition to the PRACH configuration related information.Since DL/UL frequency bands may differ, the PBCH may transmit DL/ULsystem bandwidth information and transmit a numerology used for ULdata/control channel transmission, i.e., a subcarrier spacing, a CPlength, a subframe length, a symbol length, or the number of symbolsconstituting a subframe, as well as a numerology used for DLdata/control channel reception.

A.3.2. RACH Procedure

FIG. 10 illustrates an RACH procedure.

Hereinafter, an RACH procedure of the UE for detecting an SS such as aPSS/SSS to acquire DL time/frequency synchronization and a cell ID andthen receiving a PBCH to acquire UL synchronization will be described.As described with reference to FIG. 3, the RACH procedure in LTE/LTE-Abroadly includes 4-step message exchange.

1) S1010. Msg1 (UE to eNB): A random access preamble on an RACH on UL.

2) S1020. Msg2 (eNB to UE): An RAR including a UL grant about a DL-SCH,a temporary UE ID, and a TA command.

3) S1030. Msg3 (UE to eNB): First scheduled UL transmission on a UL-SCH.UE ID transfer.

4) S1040. Msg4 (eNB to UE): Contention resolution on DL (a UE ID isechoed). RRC connection establishment.

If the RACH procedure is ended, the UE is connected to a correspondingcell.

The RACH procedure of the NR system for which a plurality of differentuse cases and/or a plurality of numerologies can be used needs to bedifferentiated from the RACH procedure of the legacy LTE/LTE-A system.

Upon acquiring the DL synchronization and the cell ID by detecting theSS, the UE may acquire PRACH configuration information through PBCHreception and acquire information about the PRACH resource as mentionedabove in Section A.3.3. Then, the UE may transmit a PRACH preamble onthe PRACH resource using the PRACH configuration information.

When the UE transmits the PRACH preamble, i.e., when the UE transmitsmessage 1 (Msg1), the following information is transmitted together withMsg1. As another scheme, the following information may be transmittedafter message 3 (Msg3) is transmitted or RRC connection setup isperformed.

A service type, a use case (mMTC, eMBB, and/or URLLC), and/or asupported subcarrier spacing.

Preferred beam index(es) and/or BRS port number(s).

Information about the service type and/or the use case and informationabout the supported subcarrier spacing may be reported in a combinedformat. In addition, information about a plurality of service typesand/or a plurality of use cases or a plurality of supported subcarrierspacings may be transmitted. If the UE supports a plurality of servicetypes and/or a plurality of use cases or a plurality of supportedsubcarrier spacings, the UE may transmit information about a servicetype and/or a use case that the UE desires to receive mostpreferentially and priority information about the supported subcarrierspacings. Even when the UE supports a plurality of service types and/ora plurality of use cases, only a service and a subcarrier space that theUE desires to preferentially receive may be requested.

As a response to the PRACH message 1 (Msg1), a TRP may transmit an RARand the RAR message transfers a temporary RNTI (T-RNTI) and thentime/frequency information through which the UE can transmit Msg3. TheRAR is a message transmitted as a response to Msg1 of the UE. The TRPtransmits the RAR in consideration of information about a service typeand/or a use case, or a supported subcarrier spacing that the UE hasreported through Msg1. A method of considering the information about theservice type, the use case, and/or the subcarrier spacing in the RAR maybe as follows. A method described hereinbelow may be used for a normalRACH procedure even though the method is not for the purpose ofadditionally considering the service type, the use case, and/or thesubcarrier spacing.

-   -   Option A.3.2-1

RACH Msg1 including information about a requested service type, usecase, and/or subcarrier spacing may be transmitted and the TRP transmitsan RAR in consideration of this information. An RAR including UL grantinformation for allocating a UL resource on which Msg3 for a specificRACH preamble sequence can be transmitted may be transmitted on a DLshared channel. When the UE allocates the UL resource on which Msg3 canbe transmitted, the TRP allocates the resource in a band to which thesubcarrier spacing, the service type, and/or the use case requested bythe UE is applied. In addition, the TRP transmits information about anumerology available for Msg3 transmission by the UE as well.

If the subcarrier spacing, the service type, and/or the use caserequested by the UE are not applied at a corresponding timing in acorresponding system, the TRP may command the UE to transmit Msg3 usinga numerology used for SS transmission or a numerology used for PRACH(Msg1) transmission. When the UE does not support a numerology indicatedby an RAR to be used for Msg3 transmission, the UE automaticallytransmits Msg3 using the numerology used for SS transmission in acorresponding band or the numerology used for PRACH (Msg1) transmission.

Alternatively, when UL grant information is transmitted through the RAR,the TRP may designate a numerology (e.g., a subcarrier spacing) which isto be used on a corresponding resource together with information about aUL time/frequency resource on which Msg3 is to be transmitted withrespect to each preamble sequence, i.e., each UE. In addition, timingadvance (TA) information is transmitted in the RAR and the TRP maytransmit a different TA value according to subcarrier spacing. Forexample, if the TA is 2 T_(s) based on a subcarrier spacing of 15 kHz,then a TA value in a band in which a subcarrier spacing of 30 kHz isused is 4 T_(s). To transmit Msg3, the UE receives a UL resourceallocated in a carrier or a subband to which the subcarrier spacing,service type, and/or use case requested thereby is applied. If a UE IDis separately managed with respect to each carrier or each use case, atemporary UE ID for transmitting Msg3 may also be received in thecorresponding carrier or subband. The UE may receive an allocated C-RNTIin Msg4 in which contention resolution occurs and the C-RNTI may also beallocated with respect to each use case.

Although the UE has transmitted Msg1, if the UE fails to receive theRAR, the UE may repeatedly attempt to transmit Msg1 on a PRACH resource.A UE that transmits Msg3 by moving to a carrier suitable for asubcarrier spacing, a service type, and/or a use case desired therebyafter receiving the RAR, a UE that fails to successfully receive Msg4,or a UE that has not succeeded in connection because the UE is notfinally selected after contention resolution may perform the followingoperations.

1) Alt 1: The UE may reattempt to transmit RACH Msg1 on a PRACH resourceon which a PRACH has first been transmitted.

2) Alt 2: In preparation for the above-mentioned cases, the TRP mayallocate a plurality of UL resources for Msg3 transmission (in eachcarrier). For example, if the UE fails to successfully receive Msg4 orthe UE has not succeeded in connection because the UE is not finallyselected in contention resolution, the UE may attempt to transmit Msg3using a UL resource allocated for Msg3 transmission.

-   -   Option A.3.2-2

If a subcarrier spacing, a service type, and/or a use case of the UE istransmitted through RACH Msg1, contention with other UEs may beproblematic. As another method considering the subcarrier spacing, theservice type, and/or the use case of the UE, which is different fromOption A.3.2-1, Option A.3.2-2 causes the UE to transmit an RACH in Msg1and the TRP to transmit an RAR in Msg2 similarly to a legacy LTE RACHprocedure. In addition, the UE may report information about thesubcarrier spacing, the service type, and/or the use case to the TRP inMsg3. A plurality of information may be reported and information abouteach subcarrier spacing, each service type, and/or each use case may betransmitted in Msg4. That is, even when the TA value has beentransmitted in Msg2, the TA value may be additionally transmittedaccording to a numerology, resource information/carrier information towhich a specific use case is applied may be transmitted, and anadditional C-RNTI may be allocated to the UE in each carrier throughMsg4. In other words, the C-RNTI per use case or per carrier may beallocated. Upon receiving information about Msg4, the UE may receive aservice by moving to a specific carrier or through retuning according toa subcarrier spacing, a service type, and/or a use case desired thereby.If the UE should receive a service by moving to a carrier, for example,if the UE moves to a partial carrier or a subband of a system bandalthough the UE adjusts coarse synchronization by receiving an SS of thesystem band, the TRP may additionally inform the UE of RS informationneeded when the UE performs fine synchronization, particularly, trackingRS information, and dedicatedly inform the UE of a resource on which theUE can transmit a simple RACH for UL tuning in a corresponding carrier.If the UE performs an RACH procedure from the beginning in order toadjust UL synchronization, since overhead greatly increases, the TRPinforms the UE of a dedicated resource for the simple RACH. Thisinformation may be transmitted in Msg4. The simple RACH means a signalthat the UE transmits to adjust UL synchronization in a connected stateand only the TA command may be transmitted in the RAR that the UEreceives as a response to the simple RACH. The simple RACH may betransmitted using an RACH subcarrier spacing tied to a subcarrierspacing indicated for data transmission in Msg4.

A.3.3. PRACH Numerology

When the UE transmits PRACH Msg1 in a PRACH time-frequency, if a defaultnumerology of a system has been defined, the UE may transmit PRACH Msg1using the default numerology. Transmitting PRACH Msg1 using the defaultnumerology implies that RACH Msg1 is transmitted using an RACH Msg1numerology associated with the default numerology. Herein, arepresentative example of the numerology may be, particularly, asubcarrier spacing. For example, RACH Msg1 in a band using a subcarrierspacing (SC) of 15 kHz as the default SC may be transmitted using an SCof 1.25 kHz and RACH Msg1 in a band using an SC of 30 kHz as the defaultSC may be transmitted using an SC of 2.5 kHz.

Specific parameter sets may be defined according to transmissionbandwidth for an SS of NR (hereinafter, an NR-SS) and the default SC.For example, the following parameter sets may be associated with thedefault SC and a maximum possible transmission bandwidth for the NR-SS.

Parameter set #W associated with an SC of 15 kHz and an NR-SStransmission bandwidth not greater than 5 MHz.

Parameter set #X associated with an SC of 30 kHz and an NR-SStransmission bandwidth not greater than 10 MHz.

Parameter set #Y associated with an SC of 120 kHz and an NR-SStransmission bandwidth not greater than 40 MHz.

Parameter set #Z associated with an SC of 240 kHz and an NR-SStransmission bandwidth not greater than 80 MHz.

PRACH Sequence Length

When reuse/re-farming of LTE deployment is considered, it is better touse a PRACH preamble of a long sequence in order to support wide cellcoverage and a sufficient number of preambles within wide cell coverage.Accordingly, it is better to support a PRACH preamble of a long lengthin NR in a frequency band at least below 6 GHz.

The followings are considered in designing a PRACH sequence.

A high Doppler frequency offset for high-speed requirements (a maximumof 500 km/h).

Unified design of FDD and TDD slot structures.

A beam scanning operation of a PRACH preamble when beam correspondencedoes not hold at a gNB.

As mentioned previously, an RACH preamble of a long sequence may besupported in an NR in a band below 6 GHz to support wide coverage.Meanwhile, according to requirements of the NR system, since a maximummobile speed to be supported is about 500 km/h, a PRACH sequence of ashort length may be introduced to provide robustness of a Dopplerfrequency offset. That is, although a short sequence has greatusefulness in a band above 6 GHz, the short sequence needs to besupported even in a band below 6 GHz to support a very high speed of 500km/h. As described above, in order for the gNB to support a dynamic TDDand beam scanning operation in a band above 6 GHz, NR may support thePRACH sequence of a short length and repetition may be introduced forthe beam scanning operation and/or energy accumulation. For example,when the short sequence is used, the PRACH sequence is desirablyconfigured by repetition of short sequence(s). In this case, CP overheadis not needed between repeated sequences. For the RACH preamble,multiple sequence lengths per band may be used in a band at least below6 GHz.

FIG. 11 illustrates a performance effect of Doppler frequency spreadaccording to SC. Particularly, FIG. 11 illustrates simulation results ofevaluating the performance effect of Doppler frequency spread accordingto sequence length (i.e., SC) at a speed of 500 km/h. In FIG. 11, CDL-Crepresents a clustered delay line-C.

According to the simulation results, an SC of an RACH preamble should begreater than at least 5 kHz to protect a UE having the highest speed.FIG. 11 shows that the performance levels of PRACH sequences having SCsof 5 kHz, 7.5 kHz, and 15 kHz are similar to each other at a speed of500 km/h and may have freedom to select an SC of a PRACH sequence.Assuming that these three candidate SCs provide similar performancelevels, it is better to determine an SC for an RACH preamble sequence inconsideration of the dynamic TDD and/or beam scanning operation at thegNB, system overhead, system flexibility, and/or efficiency. The PRACHsequence of 5 kHz may be inefficient in terms of overhead consumed forthe beam scanning operation and support of dynamic TDD. Since 5 kHz isthe least among the three SCs, i.e., 5 kHz, 7.5 kHz and 15 kHz, the RACHpreamble of an SC of 5 kHz is longest in the time domain and thus timeused for RACH transmission increases. In addition, since the gNB shouldallocate an RACH resource for multiple reception beams, the amount ofnecessary resource allocation increases relative to other SCs.Therefore, using of an SC of 7.5 kHz for the PRACH sequence may beconsidered. Meanwhile, if the PRACH sequence is too short in the timedomain, for example, if an SC is 15 kHz, the number of codes may beinsufficient. In consideration of this situation, an SC of 7.5 kHz maybe used for a short sequence of the RACH preamble in a frequency bandsupporting an SC of 15 kHz of the NR-SS. For example, in the case of acarrier frequency below 4 GHz, 7.5 kHz may be used as an SC for a shortRACH preamble sequence. A default numerology may representatively referto a numerology used to transmit an SS and a PBCH. As mentioned above,the default numerology may be referred to as the reference numerology.The default numerology may be defined with respect to each frequencyband or each frequency range. Broadly, an SC of 15 kHz or an SC of 30kHz may be defined below 6 GHz based on 6 GHz as a default SC of SS/PBCHtransmission and an SC of 120 kHz or an SC of 240 kHz may be definedabove 6 GHz as the default SC of SS/PBCH transmission. In detail, the SCof 15 kHz may be used in a band below 3 GHz, the SC of 30 kHz may beused in a band above 3 GHz and below 6 GHz, the SC of 120 kHz may beused in a band above 6 GHz and below a predetermined band, and the SC of240 kHz may be used in a band above the predetermined band. Therefore,in order to detect the SS in a specific band, the UE may attempt todetect the SS using the default SC defined for SS transmission in thecorresponding band. The UE may receive the SS/PBCH and receive minimumSI including RACH configuration. An SC for RACH Msg1 transmission mayalso be tied to an SC of the SS/PBCH. For example, when the SC of theSS/PBCH is 15 kHz, the SC of RACH Msg1 may be set to 1.25 kHz and, whenthe SC of the SS/PBCH is 30 kHz, the SC of RACH Msg1 may be set to 2.5kHz. When the SC of the SS/PBCH is 120 kHz, the SC of RACH Msg1 SC maybe set to 10 kHz and, when the SC of the SS/PBCH is 240 kHz, the SC ofRACH Msg1 may be set to 20 kHz. Notably, if the gNB transmits theSS/PBCH through multiple beams, beam correspondence of the gNB may notbe supported or the (time) symbol length of an RACH Msg1 sequence, i.e.,the (time) symbol length of an RACH preamble, needs to be reduced to berepeatedly transmitted in the time domain in order to support ahigh-speed UE. For this purpose, the symbol length of the RACH preamblemay be reduced by widening the SC of the RACH preamble. Typically, ifthe SC of the RACH preamble is widened, the frequency size of the RACHpreamble is extended in proportion to the size of a subcarrier. However,for the efficiency of a radio resource, it is difficult to indefinitelyincrease the size of an RACH resource. Accordingly, if the frequencysize of the RACH resource is limited, the length of an RACH preamblesequence decreases as the SC of the RACH preamble increases. If the gNBperforms beam sweeping to receive RACH Msg1, the UE may perform repeatedtransmission using a frequency resource of RACH Msg1, i.e., a frequencyresource such as the RACH preamble. If the SC of RACH Msg1 is small,since a long sequence occupying a time of 1 ms should be repeatedlytransmitted, overhead increases and a channel characteristic may differaccording to time. Therefore, it is efficient to repeatedly transmit anRACH sequence having a wide SC and a short time length. Since energy iscollected when a signal is transmitted for a long time and then coveragewill be extended, a long sequence is needed for coverage extension.Accordingly, unlike legacy LTE that supports only an RACH preamble of along sequence spanning a subframe of a 1-ms time length, transmission ofRACH Msg1 in a repeated form of a short sequence may be supported in NRin addition to the preamble of a long sequence. To this end, a pluralityof RACH Msg1 numerologies is defined with respect to one default SC. Asdescribed previously, a sequence having an SC of 7.5 kHz may beconsidered as an RACH sequence candidate of a short sequence.Consequently, a plurality of PRACH sequences may be mapped to onedefault SC. For example, a long RACH sequence and a short RACH sequencemay be defined with respect to one UL default SC.

Unless additionally signaled, a DL default numerology and a UL defaultnumerology may be set to be equal. For example, when the TRP informs theUE of RACH configuration information, the unit of an RACH resource forRACH transmission is configured based on DL-UL default numerologies.That is, a UL RACH resource is configured based on a DL slot length anda DL symbol length.

If a DL numerology is different from a UL numerology, for example, if anumerology available for SS/PBCH transmission is different from anumerology of a UL RACH resource and PUSCH scheduling (at least Msg3), aUL slot length should be particularly indicated by SI. That is, therelationship between the UL slot length, slot indexes allocated as theRACH resource, and DL slots/indexes should be provided by the SI. The UEmay be accurately aware of the location of the RACH resource through theSI. However, if no additional signaling is given, the UE may assume thatthe DL slot length is equal to the UL slot length. In addition, thenetwork may transmit RACH resource configuration information under theassumption that the UL slot length is identical to the DL slot length.

The following table lists NR PRACH SCs and parameters in a band having adefault SC of 15 kHz.

TABLE 2 Preamble Subcarrier CP Preamble format spacing Bandwidthduration duration Long #1 1.25 kHz 1.08 MHz 103 us 800 us Long #2 690 us800 us Long #3 203 us 1600 us Long #4 690 us 1600 us Short #1  7.5 kHz22.2 us N*66.7 us Short #2 66.7 us N*66.7 us Short #3 133.3 us N*66.7 us

An NR PRACH SC in a band which does not have a default SC of 15 kHz isscaled according to a default SC value. A CP and a preamble durationshould be provided through RACH configuration and an RACH Msg1 SC istied to an RACH time/frequency resource for RACH Msg1 transmission. TheUE repeatedly transmits RACH Msg1 using a short sequence on an RACHresource on which repetition is permitted and transmits RACH Msg1 usinga long sequence on an RACH resource on which repetition is notpermitted.

Hereinabove, the present invention has been described under theassumption that bands below 6 GHz are divided into frequency band(s)having a default SC of 15 kHz and frequency band(s) having a default SCof 30 kHz and bands above 6 GHz are divided into frequency band(s)having a default SC of 120 kHz and frequency band(s) having a default SCof 240 kHz. However, when all bands below 6 GHz support one default SC,for example, when a default SC below 6 GHz is 15 kHz, a plurality of SCsof long sequences for the RACH preamble may be defined per default SC.For example, a long sequence having an SC of 1.25 kHz and a longsequence having an SC of 2.5 kHz may be supported for the default SCused below 6 GHz. The default SC is inevitably associated with a minimumbandwidth (BW) of a system because a band in which a PSS/SSS/PBCH istransmitted will be limited to the minimum BW. In spite of this reason,an SC used for data transmission/reception in a corresponding system maydiffer from the default SC according to service requirements. In otherwords, even if the default SC is 15 kHz, an RACH preamble of 1.25 kHzmay be used in a band/cell in which an SC used mainly for a data serviceis 15 kHz and an RACH preamble of 2.5 kHz may be used in a band/cell inwhich an SC used mainly for a data service is 30 kHz. The TRP maypre-designate an SC value of the long sequence through signaling of RACHconfiguration. Likewise, a short sequence may also have two candidatesand an SC value for the short sequence may also be designated throughsignaling of RACH configuration. If the SC of the RACH preamble isindicated, the UE may become implicitly aware of the SC used for thedata service in a corresponding cell and use an SC associated with theRACH SC as an SC of Msg3 transmission unless additionally signaled. Forexample, a preamble SC of 1.25 kHz (i.e., an RACH Msg1 SC of 1.25 kHz)may be associated with a data SC of 15 kHz and a preamble SC of 2.5 kHzmay be associated with a data SC of 30 kHz. When an SC of 1.25 kHz isindicated through RACH configuration, the UE uses an SC of 15 kHz forMsg3 transmission and, when an SC of 2.5 kHz is indicated through RACHconfiguration, the UE uses an SC of 30 kHz for Msg3 transmission. Inthis case, the SC of 1.25 kHz and the SC of 2.5 kHz are examples ofpreamble SCs, i.e., examples of SCs for RACH Msg1 transmission, andother values may be used. Even if different SC values are used aspreamble SCs, the different SC preamble values are configured inassociation with SC values of data.

When an association relationship is not configured between a default SCand an RACH Msg1 SC, a method of determining an PRACH transmissionnumerology is described below.

The UE may transmit/receive RACH Msg1 and then Msg2, Msg3, or Msg4 usinga numerology used for PSS/SSS detection. If a numerology to be used forDL data and UL data transmission/reception after a PRACH procedurebecomes different, a numerology used for data transmission/reception maybe signaled in RACH Msg2 or RACH Msg4.

If a numerology used for PSS/SSS transmission is different from anumerology used for PBCH transmission or if a PSS/SSS is multiplexedwith a PBCH through TDM, the UE may conform to the numerology used forPBCH transmission as a numerology used for PRACH transmission. Inconsideration of multiplexing of the PBCH with other data andmultiplexing of a PRACH resource with other data, the numerology usedfor PRACH transmission may conform to the numerology used for PBCHtransmission.

Next, the PRACH response (i.e., Msg2) as a response to Msg1 may betransmitted based on a numerology used when the UE transmits PRACH Msg1and the UE may transmit information about one or more numerologies andabout use cases that the UE desires to use in Msg1. Upon transmitting anRAR for PRACH Msg1, the eNB may designate and transmit a numerology tobe used for Msg3 and Msg4 transmission. Alternatively, a numerology tobe used for data transmission/reception may be indicated by the RAR.When information about an additional numerology is not transmitted, theUE may transmit/receive subsequent messages and DL/UL signals using anumerology associated with a numerology used thereby for PRACH Msg1.

There may be some options for an RACH numerology. The first option is toconform to an SS block numerology. There may be predefined implicitmapping to a PSS/SSS numerology and/or a PBCH numerology may beperformed based on the SS block numerology. That is, the UE mayimplicitly determine a PRACH numerology based on a detected PSS/SSSand/or PBCH numerology without an explicit signal for the PRACHnumerology. If PRACH configuration is provided in the form of a shareddata channel similarly to the LTE system using a common search space ina DL control region, this option will be proper because the UE has noinformation about a numerology for data/control. If this option is used,at least RACH Msg1 and RACH Msg2 may share the same numerology or may betied to the PSS/SSS numerology and/or the PBCH numerology. Anotheroption is to signal the RACH numerology through essential SI. PRACHconfiguration provides numerologies for the PRACH and the RAR.Basically, a numerology of Msg3 may conform to a numerology of Msg1 anda numerology of Msg4 may conform to a numerology of Msg2 unless the RARindicates the numerologies of Msg3 and Msg4. Msg4 may indicate anumerology for a later DL/UL data/control channel.

If the RACH procedure, i.e., a PRACH procedure, is completed, the UEacquires DL/UL time/frequency synchronization, a cell ID, a cellassociated UE ID, and other SI and is ready to receive DL data andtransmit UL data. Accordingly, if the RACH procedure, i.e., the PRACHprocedure, is completed, the UE is in an RRC_connected state and may endthe initial access procedure.

B. Minimum SI Delivery

Hereinafter, details of how SI is delivered will be discussed. A PBCHdelivers a part of minimum SI. RMSI is transmitted on a PDSCH and thePBCH may provide configuration information of the RMSI in order to causethe UE to retrieve the SI.

<B.1. Signaling of Configuration Information for RMSI>

There may be a method of providing the configuration information of theRMSI. For example, the PBCH may provide a control channel search spaceor scheduling allocation for the RMSI. If the PBCH provides the controlchannel search space such as a common search space (CSS) having abeam-specific characteristic in mmWave, the UE searches for a controlchannel to receives minimum SI. Although this method may consume thecontrol channel search space, the method provides much flexibility tothe NR system in terms of resource allocation, an MCS, etc.Alternatively, although a specific search space may not be necessary,the search space may be confined within an SS block transmissionbandwidth. For SI reception, the NR system may configure non-UEdedicated search spaces for control channels, which may be SS-blockspecific or UE-group specific. A set of these search spaces may bepredefined by communication standard and an NR-PBCH may signal specificset(s) of search spaces for the RMSI. Another method serves to cause thePBCH to provide scheduling allocation of the RMSI including resourceallocation, an applied MCS, etc. In consideration of the fact that thecontent of the PBCH is not frequently changed, resources for the RMSImay be semi-statically reserved using a fixed MCS in a system. To reducesignaling overhead within the PBCH, a part of the configurationinformation may be specified by a communication specification and the UEmay derive accurate configuration information by a combination ofsignaling within the PBCH and the communication specification.

The information that can be specified by the communication specificationfor minimum SI reception includes numerologies, candidate MCS sets,control search space candidates, and/or subband candidates.

<B.2. Content of Configuration Information for RMSI>

According to signaling options of the configuration information for theRMSI, the content of the configuration information about the RMSI may beas follows.

-   -   Option B.2-1) The PBCH provides information about the control        channel search space.

The PBCH may carry the information about the control channel searchspace in which a PDCCH for scheduling the RMSI (hereinafter, an RMSIPDCCH) is transmitted, for example, information about a frequencyresource on which the RMSI PDCCH may be present. The PBCH may carryinformation indicating that the control channel search space may be aCSS or a beam-specific space and/or numerology information. Thenumerology information may include, for example, an SC of the controlchannel, possibly, an SC for a PDSCH carrying the RMSI (this informationmay also be signaled within a control channel (or DCI) rather than thePBCH), a slot or a min-slot which is a time interval in which the UEshould blind-detect the control channel (or DCI) in the time domain,and/or timing information about a timing at which minimum SI can betransmitted. The timing information includes, for example, a minimum SIperiodicity, a timing offset from detection of the PBCH, and/or a timingwindow in which minimum SI can be transmitted. The information carriedby the control channel (or DCI) includes, for example, time-frequencyresource allocation information and/or an MCS.

-   -   Option B.2-2) The PBCH provides scheduling allocation        information.

The scheduling allocation information includes time-frequency resourceallocation information, an MCS, and/or numerology information of minimumSI. The numerology information of the minimum SI includes, for example,an SC of a PDSCH carrying the minimum SI, a slot or mini-slot length inthe time domain, the number of symbols occupied by the PDSCH carryingthe minimum SI, and/or timing information about a timing at which theminimum SI can be transmitted. The timing information includes a minimumSI periodicity, a timing offset from detection of the PBCH, and/or atiming window in which the minimum SI can be transmitted.

Since the RMSI is provided through the PDSCH, a numerology for the RMSI,particularly, an SC for the RMSI, should be identical to an SC for thePDSCH. To reduce overhead in the PBCH, default numerologies for aPDCCH/PDSCH/PUSCH/PUCCH may be defined. The default numerologies for thePDCCH/PDSCH/PUSCH/PUCCH may be provided through a broadcast channel suchas the PBCH or may be predefined in the communication standard withrespect to each frequency range. The SC for the RMSI may conform to thedefault numerologies for the PDCCH/PDSCH.

FIG. 12 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

The transmitting device 10 and the receiving device 20 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedexamples of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 10 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into K layers through demultiplexing, channel coding,scrambling, and modulation. The coded data stream is also referred to asa codeword and is equivalent to a transport block which is a data blockprovided by a MAC layer. One transport block (TB) is coded into onecodeword and each codeword is transmitted to the receiving device in theform of one or more layers. For frequency up-conversion, the RF unit 13may include an oscillator. The RF unit 13 may include N_(t) (where N_(t)is a positive integer) transmit antennas.

A signal processing process of the receiving device 20 is the reverse ofthe signal processing process of the transmitting device 10. Undercontrol of the processor 21, the RF unit 23 of the receiving device 20receives radio signals transmitted by the transmitting device 10. The RFunit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 10 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 20. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 20 and enables the receiving device 20 to derivechannel estimation for the antenna, irrespective of whether the channelrepresents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the examples of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe examples of the present invention, an eNB operates as the receivingdevice 20 in UL and as the transmitting device 10 in DL. Hereinafter, aprocessor, an RF unit, and a memory included in the UE will be referredto as a UE processor, a UE RF unit, and a UE memory, respectively, and aprocessor, an RF unit, and a memory included in the eNB will be referredto as an eNB processor, an eNB RF unit, and an eNB memory, respectively.

The eNB processor and the UE processor may perform an initial accessprocedure according to a proposal of the present invention. The eNBprocessor may control the eNB RF unit to transmit a PSS, an SSS, and aPBCH according to the proposal of the present invention. The UEprocessor may control detect the PSS, the SSS, and the PBCH bycontrolling the UE RF unit and acquire DL time/frequency synchronizationwith a cell according to the proposal of the present invention. The UEprocessor may perform an RACH procedure for UL synchronization with thecell according to the proposal of the present invention. The UEprocessor may control the UE RF unit to transmit RACH Msg1 according tothe proposal of the present invention. The eNB processor may control theeNB RF unit to receive RACH Msg1 and control the eNB RF unit to transmitRACH Msg2 according to the proposal of the present invention. The UEprocessor may control the UE RF unit to receive RACH Msg2 and controlthe UE RF unit to transmit RACH Msg3 according to the proposal of thepresent invention. The eNB processor may control the eNB RF unit toreceive RACH Msg3 and control the UE RF unit to transmit RACH Msg4according to the proposal of the present invention.

The eNB processor may control the eNB RF unit to transmit essential SIaccording to the proposal of the present invention. The UE processor maycontrol the UE RF unit to receive the essential SI according to theproposal of the present invention.

As described above, the detailed description of the preferred examplesof the present invention has been given to enable those skilled in theart to implement and practice the invention. Although the invention hasbeen described with reference to exemplary examples, those skilled inthe art will appreciate that various modifications and variations can bemade in the present invention without departing from the spirit or scopeof the invention described in the appended claims. Accordingly, theinvention should not be limited to the specific examples describedherein, but should be accorded the broadest scope consistent with theprinciples and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The examples of the present invention are applicable to a base station,a user equipment, or other devices in a wireless communication system.

What is claimed is:
 1. A method of receiving a downlink signal by a userequipment in a wireless communication system, the method comprising:detecting, in a frequency band, a broadcast channel using a firstsubcarrier spacing defined for a frequency range to which the frequencyband belongs; and receiving, in the frequency band, a downlink datachannel carrying system information using a second subcarrier spacing,based on information on the second subcarrier spacing carried by thebroadcast channel.
 2. The method of claim 1, further comprisingreceiving the downlink data channel carrying the system informationusing the first subcarrier spacing when the information on the secondsubcarrier spacing is not present within the broadcast channel.
 3. Themethod of claim 1, wherein the broadcast channel carries configurationinformation on a search space for receiving control information of thedownlink data channel or time resource information on a time resource onwhich the system information can be transmitted, and wherein the timeresource information includes a periodicity at which the systeminformation can be transmitted, a time offset between the broadcastchannel and a time at which the system information can be transmitted,or a time window in which the system information can be transmitted. 4.The method of claim 1, wherein the information on the second subcarrierspacing is information indicating one of candidate subcarrier spacingsdefined for each carrier range for a data channel.
 5. The method ofclaim 1, wherein the broadcast channel carries information on asubcarrier spacing for a random access channel.
 6. A method oftransmitting a downlink signal by a base station in a wirelesscommunication system, the method comprising: transmitting, in afrequency band, a broadcast channel using a first subcarrier spacingdefined for a frequency range to which the frequency band belongs; andtransmitting, in the frequency band, a downlink data channel carryingsystem information using a second subcarrier spacing, based oninformation on the second subcarrier spacing carried by the broadcastchannel.
 7. The method of claim 6, further comprising transmitting thedownlink data channel carrying the system information using the firstsubcarrier spacing when the information on the second subcarrier spacingis not transmitted on the broadcast channel.
 8. The method of claim 6,wherein the broadcast channel carries configuration information on asearch space for transmitting control information of the downlink datachannel or time resource information on a time resource on which thesystem information is transmitted, and wherein the time resourceinformation includes a periodicity at which the system information canbe transmitted, a time offset between the broadcast channel and a timeat which the system information can be transmitted, or a time window inwhich the system information can be transmitted.
 9. The method of claim6, wherein the information on the second subcarrier spacing isinformation indicating one of candidate subcarrier spacings defined foreach carrier range for a data channel.
 10. The method of claim 6,wherein the broadcast channel carries information on a subcarrierspacing for a random access channel.
 11. A user equipment for receivinga downlink signal in a wireless communication system, the user equipmentcomprising, a radio frequency (RF) unit, and a processor configured tocontrol the RF unit, the processor configured to: detect, in a frequencyband, a broadcast channel using a first subcarrier spacing defined for afrequency range to which the frequency band belongs; and control the RFunit to receive, in the frequency band, a downlink data channel carryingsystem information using a second subcarrier spacing, based oninformation on the second subcarrier spacing carried by the broadcastchannel.
 12. The user equipment of claim 11, wherein the processor isconfigured to control the RF unit to receive the downlink data channelcarrying the system information using the first subcarrier spacing whenthe information on the second subcarrier spacing is not present withinthe broadcast channel.
 13. The user equipment of claim 11, wherein thebroadcast channel carries configuration information on a search spacefor receiving control information of the downlink data channel or timeresource information on a time resource on which the system informationis transmitted, and wherein the time resource information includes aperiodicity at which the system information can be transmitted, a timeoffset between the broadcast channel and a time at which the systeminformation can be transmitted, or a time window in which the systeminformation can be transmitted.
 14. The user equipment of claim 11,wherein the information on the second subcarrier spacing is informationindicating one of candidate subcarrier spacings defined for each carrierrange for a data channel.
 15. The user equipment of claim 11, whereinthe broadcast channel carries information on a subcarrier spacing for arandom access channel.
 16. A base station for transmitting a downlinksignal in a wireless communication system, the base station comprising,a radio frequency (RF) unit, and a processor configured to control theRF unit, the processor configured to: control the RF unit to transmit,in a frequency band, a broadcast channel using a first subcarrierspacing defined for a frequency range to which the frequency bandbelongs; and control the RF unit to transmit, in the frequency band, adownlink data channel carrying system information using a secondsubcarrier spacing, based on information on the second subcarrierspacing carried by the broadcast channel.
 17. The base station of claim16, wherein the processor is configured to control the RF unit totransmit the downlink data channel carrying the system information usingthe first subcarrier spacing when the information on the secondsubcarrier spacing is not transmitted on the broadcast channel.
 18. Thebase station of claim 16, wherein the broadcast channel carriesconfiguration information on a search space for transmitting controlinformation of the downlink data channel or time resource information ona time resource on which the system information is transmitted, andwherein the time resource information includes a periodicity at whichthe system information can be transmitted, a time offset between thebroadcast channel and a time at which the system information can betransmitted, or a time window in which the system information can betransmitted.
 19. The base station of claim 16, wherein the informationon the second subcarrier spacing is information indicating one ofcandidate subcarrier spacings defined for each carrier range for a datachannel.
 20. The base station of claim 16, wherein the broadcast channelcarries information on a subcarrier spacing for a random access channel.